Merge branch 'master' into schema-alteration

Conflicts:
	django/db/backends/mysql/introspection.py
	django/db/backends/oracle/creation.py
	django/db/backends/postgresql_psycopg2/creation.py
	django/db/models/base.py
	django/db/models/loading.py

114 files changed, 979 insertions, 642 deletions

diff --git a/django/conf/global_settings.py b/django/conf/global_settings.py
index 7882b21b9b..364aa10320 100644
--- a/django/conf/global_settings.py
+++ b/django/conf/global_settings.py
@@ -184,6 +184,7 @@ EMAIL_PORT = 25
 EMAIL_HOST_USER = ''
 EMAIL_HOST_PASSWORD = ''
 EMAIL_USE_TLS = False
+EMAIL_USE_SSL = False
 
 # List of strings representing installed apps.
 INSTALLED_APPS = ()
diff --git a/django/conf/locale/__init__.py b/django/conf/locale/__init__.py
index df6ab07663..59927b2397 100644
--- a/django/conf/locale/__init__.py
+++ b/django/conf/locale/__init__.py
@@ -279,7 +279,7 @@ LANG_INFO = {
         'bidi': False,
         'code': 'lt',
         'name': 'Lithuanian',
-        'name_local': 'Lithuanian',
+        'name_local': 'Lietuviškai',
     },
     'lv': {
         'bidi': False,
@@ -399,7 +399,7 @@ LANG_INFO = {
         'bidi': False,
         'code': 'sq',
         'name': 'Albanian',
-        'name_local': 'Albanian',
+        'name_local': 'shqip',
     },
     'sr': {
         'bidi': False,
@@ -441,7 +441,7 @@ LANG_INFO = {
         'bidi': False,
         'code': 'th',
         'name': 'Thai',
-        'name_local': 'Thai',
+        'name_local': 'ภาษาไทย',
     },
     'tr': {
         'bidi': False,
@@ -477,7 +477,7 @@ LANG_INFO = {
         'bidi': False,
         'code': 'vi',
         'name': 'Vietnamese',
-        'name_local': 'Vietnamese',
+        'name_local': 'Tiếng Việt',
     },
     'zh-cn': {
         'bidi': False,
diff --git a/django/conf/locale/en/LC_MESSAGES/django.po b/django/conf/locale/en/LC_MESSAGES/django.po
index 371f0af2ab..f8069f07d2 100644
--- a/django/conf/locale/en/LC_MESSAGES/django.po
+++ b/django/conf/locale/en/LC_MESSAGES/django.po
@@ -4,7 +4,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: Django\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2013-05-25 14:27+0200\n"
+"POT-Creation-Date: 2013-06-11 18:44+0200\n"
 "PO-Revision-Date: 2010-05-13 15:35+0200\n"
 "Last-Translator: Django team\n"
 "Language-Team: English <en@li.org>\n"
@@ -699,11 +699,22 @@ msgstr ""
 msgid "Enter a list of values."
 msgstr ""
 
-#: forms/forms.py:158
+#. Translators: This is the default suffix added to form field labels
+#: forms/forms.py:90
+msgid ":"
+msgstr ""
+
+#: forms/forms.py:159
 #, python-format
 msgid "(Hidden field %(name)s) %(error)s"
 msgstr ""
 
+#. Translators: If found as last label character, these punctuation
+#. characters will prevent the default label_suffix to be appended to the label
+#: forms/forms.py:525
+msgid ":?.!"
+msgstr ""
+
 #: forms/formsets.py:310
 #, python-format
 msgid "Please submit %d or fewer forms."
diff --git a/django/contrib/admin/helpers.py b/django/contrib/admin/helpers.py
index 320d3267a7..3ffb85e6c6 100644
--- a/django/contrib/admin/helpers.py
+++ b/django/contrib/admin/helpers.py
@@ -266,10 +266,12 @@ class InlineAdminForm(AdminForm):
             yield InlineFieldset(self.formset, self.form, name,
                 self.readonly_fields, model_admin=self.model_admin, **options)
 
-    def has_auto_field(self):
-        if self.form._meta.model._meta.has_auto_field:
+    def needs_explicit_pk_field(self):
+        # Auto fields are editable (oddly), so need to check for auto or non-editable pk
+        if self.form._meta.model._meta.has_auto_field or not self.form._meta.model._meta.pk.editable:
             return True
-        # Also search any parents for an auto field.
+        # Also search any parents for an auto field. (The pk info is propagated to child
+        # models so that does not need to be checked in parents.)
         for parent in self.form._meta.model._meta.get_parent_list():
             if parent._meta.has_auto_field:
                 return True
diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index 9c92f7ae9c..afc7cfc5bd 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -771,12 +771,10 @@ class ModelAdmin(BaseModelAdmin):
         Returns the preserved filters querystring.
         """
 
-        # FIXME: We can remove that getattr as soon as #20619 is fixed.
-        match = getattr(request, 'resolver_match', None)
-
+        match = request.resolver_match
         if self.preserve_filters and match:
             opts = self.model._meta
-            current_url = '%s:%s' % (match.namespace, match.url_name)
+            current_url = '%s:%s' % (match.app_name, match.url_name)
             changelist_url = 'admin:%s_%s_changelist' % (opts.app_label, opts.model_name)
             if current_url == changelist_url:
                 preserved_filters = request.GET.urlencode()
diff --git a/django/contrib/admin/sites.py b/django/contrib/admin/sites.py
index e0f43dfbfe..8abf49331b 100644
--- a/django/contrib/admin/sites.py
+++ b/django/contrib/admin/sites.py
@@ -439,6 +439,7 @@ class AdminSite(object):
         context = {
             'title': _('%s administration') % capfirst(app_label),
             'app_list': [app_dict],
+            'app_label': app_label,
         }
         context.update(extra_context or {})
 
diff --git a/django/contrib/admin/static/admin/js/admin/DateTimeShortcuts.js b/django/contrib/admin/static/admin/js/admin/DateTimeShortcuts.js
index 671af9bd78..aa12f8cf01 100644
--- a/django/contrib/admin/static/admin/js/admin/DateTimeShortcuts.js
+++ b/django/contrib/admin/static/admin/js/admin/DateTimeShortcuts.js
@@ -14,6 +14,8 @@ var DateTimeShortcuts = {
     clockDivName: 'clockbox',        // name of clock <div> that gets toggled
     clockLinkName: 'clocklink',      // name of the link that is used to toggle
     shortCutsClass: 'datetimeshortcuts', // class of the clock and cal shortcuts
+    timezoneWarningClass: 'timezonewarning', // class of the warning for timezone mismatch
+    timezoneOffset: 0,
     admin_media_prefix: '',
     init: function() {
         // Get admin_media_prefix by grabbing it off the window object. It's
@@ -26,17 +28,77 @@ var DateTimeShortcuts = {
             DateTimeShortcuts.admin_media_prefix = '/missing-admin-media-prefix/';
         }
 
+        if (window.__admin_utc_offset__ != undefined) {
+            var serverOffset = window.__admin_utc_offset__;
+            var localOffset = new Date().getTimezoneOffset() * -60;
+            DateTimeShortcuts.timezoneOffset = localOffset - serverOffset;
+        }
+
         var inputs = document.getElementsByTagName('input');
         for (i=0; i<inputs.length; i++) {
             var inp = inputs[i];
             if (inp.getAttribute('type') == 'text' && inp.className.match(/vTimeField/)) {
                 DateTimeShortcuts.addClock(inp);
+                DateTimeShortcuts.addTimezoneWarning(inp);
             }
             else if (inp.getAttribute('type') == 'text' && inp.className.match(/vDateField/)) {
                 DateTimeShortcuts.addCalendar(inp);
+                DateTimeShortcuts.addTimezoneWarning(inp);
             }
         }
     },
+    // Return the current time while accounting for the server timezone.
+    now: function() {
+        if (window.__admin_utc_offset__ != undefined) {
+            var serverOffset = window.__admin_utc_offset__;
+            var localNow = new Date();
+            var localOffset = localNow.getTimezoneOffset() * -60;
+            localNow.setTime(localNow.getTime() + 1000 * (serverOffset - localOffset));
+            return localNow;
+        } else {
+            return new Date();
+        }
+    },
+    // Add a warning when the time zone in the browser and backend do not match.
+    addTimezoneWarning: function(inp) {
+        var $ = django.jQuery;
+        var warningClass = DateTimeShortcuts.timezoneWarningClass;
+        var timezoneOffset = DateTimeShortcuts.timezoneOffset / 3600;
+
+        // Only warn if there is a time zone mismatch.
+        if (!timezoneOffset)
+            return;
+
+        // Check if warning is already there.
+        if ($(inp).siblings('.' + warningClass).length)
+            return;
+
+        var message;
+        if (timezoneOffset > 0) {
+            message = ngettext(
+                'Note: You are %s hour ahead of server time.',
+                'Note: You are %s hours ahead of server time.',
+                timezoneOffset
+            );
+        }
+        else {
+            timezoneOffset *= -1
+            message = ngettext(
+                'Note: You are %s hour behind server time.',
+                'Note: You are %s hours behind server time.',
+                timezoneOffset
+            );
+        }
+        message = interpolate(message, [timezoneOffset]);
+
+        var $warning = $('<span>');
+        $warning.attr('class', warningClass);
+        $warning.text(message);
+
+        $(inp).parent()
+            .append($('<br>'))
+            .append($warning)
+    },
     // Add clock widget to a given field
     addClock: function(inp) {
         var num = DateTimeShortcuts.clockInputs.length;
@@ -48,7 +110,7 @@ var DateTimeShortcuts = {
         shortcuts_span.className = DateTimeShortcuts.shortCutsClass;
         inp.parentNode.insertBefore(shortcuts_span, inp.nextSibling);
         var now_link = document.createElement('a');
-        now_link.setAttribute('href', "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", new Date().strftime('" + get_format('TIME_INPUT_FORMATS')[0] + "'));");
+        now_link.setAttribute('href', "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", -1);");
         now_link.appendChild(document.createTextNode(gettext('Now')));
         var clock_link = document.createElement('a');
         clock_link.setAttribute('href', 'javascript:DateTimeShortcuts.openClock(' + num + ');');
@@ -84,11 +146,10 @@ var DateTimeShortcuts = {
         quickElement('h2', clock_box, gettext('Choose a time'));
         var time_list = quickElement('ul', clock_box, '');
         time_list.className = 'timelist';
-        var time_format = get_format('TIME_INPUT_FORMATS')[0];
-        quickElement("a", quickElement("li", time_list, ""), gettext("Now"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", new Date().strftime('" + time_format + "'));");
-        quickElement("a", quickElement("li", time_list, ""), gettext("Midnight"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", new Date(1970,1,1,0,0,0,0).strftime('" + time_format + "'));");
-        quickElement("a", quickElement("li", time_list, ""), gettext("6 a.m."), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", new Date(1970,1,1,6,0,0,0).strftime('" + time_format + "'));");
-        quickElement("a", quickElement("li", time_list, ""), gettext("Noon"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", new Date(1970,1,1,12,0,0,0).strftime('" + time_format + "'));");
+        quickElement("a", quickElement("li", time_list, ""), gettext("Now"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", -1);");
+        quickElement("a", quickElement("li", time_list, ""), gettext("Midnight"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", 0);");
+        quickElement("a", quickElement("li", time_list, ""), gettext("6 a.m."), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", 6);");
+        quickElement("a", quickElement("li", time_list, ""), gettext("Noon"), "href", "javascript:DateTimeShortcuts.handleClockQuicklink(" + num + ", 12);");
 
         var cancel_p = quickElement('p', clock_box, '');
         cancel_p.className = 'calendar-cancel';
@@ -128,7 +189,14 @@ var DateTimeShortcuts = {
        removeEvent(document, 'click', DateTimeShortcuts.dismissClockFunc[num]);
     },
     handleClockQuicklink: function(num, val) {
-       DateTimeShortcuts.clockInputs[num].value = val;
+       var d;
+       if (val == -1) {
+           d = DateTimeShortcuts.now();
+       }
+       else {
+           d = new Date(1970, 1, 1, val, 0, 0, 0)
+       }
+       DateTimeShortcuts.clockInputs[num].value = d.strftime(get_format('TIME_INPUT_FORMATS')[0]);
        DateTimeShortcuts.clockInputs[num].focus();
        DateTimeShortcuts.dismissClock(num);
     },
@@ -258,7 +326,7 @@ var DateTimeShortcuts = {
         DateTimeShortcuts.calendars[num].drawNextMonth();
     },
     handleCalendarCallback: function(num) {
-        format = get_format('DATE_INPUT_FORMATS')[0];
+        var format = get_format('DATE_INPUT_FORMATS')[0];
         // the format needs to be escaped a little
         format = format.replace('\\', '\\\\');
         format = format.replace('\r', '\\r');
@@ -276,7 +344,7 @@ var DateTimeShortcuts = {
                ").style.display='none';}"].join('');
     },
     handleCalendarQuickLink: function(num, offset) {
-       var d = new Date();
+       var d = DateTimeShortcuts.now();
        d.setDate(d.getDate() + offset)
        DateTimeShortcuts.calendarInputs[num].value = d.strftime(get_format('DATE_INPUT_FORMATS')[0]);
        DateTimeShortcuts.calendarInputs[num].focus();
diff --git a/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js b/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
index 6d1748663e..c82c8c05cb 100644
--- a/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
+++ b/django/contrib/admin/static/admin/js/admin/RelatedObjectLookups.js
@@ -55,7 +55,7 @@ function dismissRelatedLookupPopup(win, chosenId) {
 function showAddAnotherPopup(triggeringLink) {
     var name = triggeringLink.id.replace(/^add_/, '');
     name = id_to_windowname(name);
-    href = triggeringLink.href
+    var href = triggeringLink.href;
     if (href.indexOf('?') == -1) {
         href += '?_popup=1';
     } else {
@@ -73,10 +73,11 @@ function dismissAddAnotherPopup(win, newId, newRepr) {
     newRepr = html_unescape(newRepr);
     var name = windowname_to_id(win.name);
     var elem = document.getElementById(name);
+    var o;
     if (elem) {
         var elemName = elem.nodeName.toUpperCase();
         if (elemName == 'SELECT') {
-            var o = new Option(newRepr, newId);
+            o = new Option(newRepr, newId);
             elem.options[elem.options.length] = o;
             o.selected = true;
         } else if (elemName == 'INPUT') {
@@ -88,8 +89,7 @@ function dismissAddAnotherPopup(win, newId, newRepr) {
         }
     } else {
         var toId = name + "_to";
-        elem = document.getElementById(toId);
-        var o = new Option(newRepr, newId);
+        o = new Option(newRepr, newId);
         SelectBox.add_to_cache(toId, o);
         SelectBox.redisplay(toId);
     }
diff --git a/django/contrib/admin/templates/admin/app_index.html b/django/contrib/admin/templates/admin/app_index.html
index 9f65357292..7aff935126 100644
--- a/django/contrib/admin/templates/admin/app_index.html
+++ b/django/contrib/admin/templates/admin/app_index.html
@@ -1,6 +1,8 @@
 {% extends "admin/index.html" %}
 {% load i18n %}
 
+{% block bodyclass %}app-{{ app_label }} {{ block.super }}{% endblock %}
+
 {% if not is_popup %}
 {% block breadcrumbs %}
 <div class="breadcrumbs">
diff --git a/django/contrib/admin/templates/admin/base.html b/django/contrib/admin/templates/admin/base.html
index 63d4419fae..9c79a4e698 100644
--- a/django/contrib/admin/templates/admin/base.html
+++ b/django/contrib/admin/templates/admin/base.html
@@ -7,6 +7,7 @@
 <!--[if lte IE 7]><link rel="stylesheet" type="text/css" href="{% block stylesheet_ie %}{% static "admin/css/ie.css" %}{% endblock %}" /><![endif]-->
 {% if LANGUAGE_BIDI %}<link rel="stylesheet" type="text/css" href="{% block stylesheet_rtl %}{% static "admin/css/rtl.css" %}{% endblock %}" />{% endif %}
 <script type="text/javascript">window.__admin_media_prefix__ = "{% filter escapejs %}{% static "admin/" %}{% endfilter %}";</script>
+<script type="text/javascript">window.__admin_utc_offset__ = "{% filter escapejs %}{% now "Z" %}{% endfilter %}";</script>
 {% block extrahead %}{% endblock %}
 {% block blockbots %}<meta name="robots" content="NONE,NOARCHIVE" />{% endblock %}
 </head>
diff --git a/django/contrib/admin/templates/admin/change_form.html b/django/contrib/admin/templates/admin/change_form.html
index d4935ed781..e35c7328f4 100644
--- a/django/contrib/admin/templates/admin/change_form.html
+++ b/django/contrib/admin/templates/admin/change_form.html
@@ -10,7 +10,7 @@
 
 {% block coltype %}colM{% endblock %}
 
-{% block bodyclass %}{{ opts.app_label }}-{{ opts.object_name.lower }} change-form{% endblock %}
+{% block bodyclass %}app-{{ opts.app_label }} model-{{ opts.object_name.lower }} change-form{% endblock %}
 
 {% if not is_popup %}
 {% block breadcrumbs %}
diff --git a/django/contrib/admin/templates/admin/change_list.html b/django/contrib/admin/templates/admin/change_list.html
index 15583d1a8c..ce5c5b37a4 100644
--- a/django/contrib/admin/templates/admin/change_list.html
+++ b/django/contrib/admin/templates/admin/change_list.html
@@ -32,7 +32,7 @@
 {% endif %}{% endif %}
 {% endblock %}
 
-{% block bodyclass %}change-list{% endblock %}
+{% block bodyclass %}app-{{ opts.app_label }} model-{{ opts.object_name.lower }} change-list{% endblock %}
 
 {% if not is_popup %}
 {% block breadcrumbs %}
diff --git a/django/contrib/admin/templates/admin/delete_confirmation.html b/django/contrib/admin/templates/admin/delete_confirmation.html
index 3ed60807b7..2e94b61485 100644
--- a/django/contrib/admin/templates/admin/delete_confirmation.html
+++ b/django/contrib/admin/templates/admin/delete_confirmation.html
@@ -1,6 +1,8 @@
 {% extends "admin/base_site.html" %}
 {% load i18n admin_urls %}
 
+{% block bodyclass %}app-{{ opts.app_label }} model-{{ opts.object_name.lower }} delete-confirmation{% endblock %}
+
 {% block breadcrumbs %}
 <div class="breadcrumbs">
 <a href="{% url 'admin:index' %}">{% trans 'Home' %}</a>
diff --git a/django/contrib/admin/templates/admin/delete_selected_confirmation.html b/django/contrib/admin/templates/admin/delete_selected_confirmation.html
index 36527dcbf5..a80f4e4a54 100644
--- a/django/contrib/admin/templates/admin/delete_selected_confirmation.html
+++ b/django/contrib/admin/templates/admin/delete_selected_confirmation.html
@@ -1,6 +1,8 @@
 {% extends "admin/base_site.html" %}
 {% load i18n l10n admin_urls %}
 
+{% block bodyclass %}app-{{ opts.app_label }} model-{{ opts.object_name.lower }} delete-confirmation delete-selected-confirmation{% endblock %}
+
 {% block breadcrumbs %}
 <div class="breadcrumbs">
 <a href="{% url 'admin:index' %}">{% trans 'Home' %}</a>
diff --git a/django/contrib/admin/templates/admin/edit_inline/stacked.html b/django/contrib/admin/templates/admin/edit_inline/stacked.html
index 2025dd8083..32917756b3 100644
--- a/django/contrib/admin/templates/admin/edit_inline/stacked.html
+++ b/django/contrib/admin/templates/admin/edit_inline/stacked.html
@@ -13,7 +13,7 @@
   {% for fieldset in inline_admin_form %}
     {% include "admin/includes/fieldset.html" %}
   {% endfor %}
-  {% if inline_admin_form.has_auto_field %}{{ inline_admin_form.pk_field.field }}{% endif %}
+  {% if inline_admin_form.needs_explicit_pk_field %}{{ inline_admin_form.pk_field.field }}{% endif %}
   {{ inline_admin_form.fk_field.field }}
 </div>{% endfor %}
 </div>
diff --git a/django/contrib/admin/templates/admin/edit_inline/tabular.html b/django/contrib/admin/templates/admin/edit_inline/tabular.html
index ca853bc989..e6097f0dce 100644
--- a/django/contrib/admin/templates/admin/edit_inline/tabular.html
+++ b/django/contrib/admin/templates/admin/edit_inline/tabular.html
@@ -29,7 +29,7 @@
           {% if inline_admin_form.original %} {{ inline_admin_form.original }}{% endif %}
           {% if inline_admin_form.show_url %}<a href="{% url 'admin:view_on_site' inline_admin_form.original_content_type_id inline_admin_form.original.pk %}">{% trans "View on site" %}</a>{% endif %}
             </p>{% endif %}
-          {% if inline_admin_form.has_auto_field %}{{ inline_admin_form.pk_field.field }}{% endif %}
+          {% if inline_admin_form.needs_explicit_pk_field %}{{ inline_admin_form.pk_field.field }}{% endif %}
           {{ inline_admin_form.fk_field.field }}
           {% spaceless %}
           {% for fieldset in inline_admin_form %}
diff --git a/django/contrib/admin/templatetags/admin_urls.py b/django/contrib/admin/templatetags/admin_urls.py
index 19da87d61f..5d9c5b5427 100644
--- a/django/contrib/admin/templatetags/admin_urls.py
+++ b/django/contrib/admin/templatetags/admin_urls.py
@@ -38,7 +38,7 @@ def add_preserved_filters(context, url, popup=False):
         except Resolver404:
             pass
         else:
-            current_url = '%s:%s' % (match.namespace, match.url_name)
+            current_url = '%s:%s' % (match.app_name, match.url_name)
             changelist_url = 'admin:%s_%s_changelist' % (opts.app_label, opts.model_name)
             if changelist_url == current_url and '_changelist_filters' in preserved_filters:
                 preserved_filters = dict(parse_qsl(preserved_filters['_changelist_filters']))
diff --git a/django/contrib/auth/admin.py b/django/contrib/auth/admin.py
index 5a1db68613..ca660606e5 100644
--- a/django/contrib/auth/admin.py
+++ b/django/contrib/auth/admin.py
@@ -70,10 +70,7 @@ class UserAdmin(admin.ModelAdmin):
         """
         defaults = {}
         if obj is None:
-            defaults.update({
-                'form': self.add_form,
-                'fields': admin.util.flatten_fieldsets(self.add_fieldsets),
-            })
+            defaults['form'] = self.add_form
         defaults.update(kwargs)
         return super(UserAdmin, self).get_form(request, obj, **defaults)
 
diff --git a/django/contrib/auth/backends.py b/django/contrib/auth/backends.py
index 05e9bfd721..6b31f72b03 100644
--- a/django/contrib/auth/backends.py
+++ b/django/contrib/auth/backends.py
@@ -5,7 +5,7 @@ from django.contrib.auth.models import Permission
 
 class ModelBackend(object):
     """
-    Authenticates against django.contrib.auth.models.User.
+    Authenticates against settings.AUTH_USER_MODEL.
     """
 
     def authenticate(self, username=None, password=None, **kwargs):
diff --git a/django/contrib/auth/hashers.py b/django/contrib/auth/hashers.py
index 87e4218a8f..7656b50437 100644
--- a/django/contrib/auth/hashers.py
+++ b/django/contrib/auth/hashers.py
@@ -22,6 +22,7 @@ UNUSABLE_PASSWORD_SUFFIX_LENGTH = 40  # number of random chars to add after UNUS
 HASHERS = None  # lazily loaded from PASSWORD_HASHERS
 PREFERRED_HASHER = None  # defaults to first item in PASSWORD_HASHERS
 
+
 @receiver(setting_changed)
 def reset_hashers(**kwargs):
     if kwargs['setting'] == 'PASSWORD_HASHERS':
@@ -34,7 +35,7 @@ def is_password_usable(encoded):
     if encoded is None or encoded.startswith(UNUSABLE_PASSWORD_PREFIX):
         return False
     try:
-        hasher = identify_hasher(encoded)
+        identify_hasher(encoded)
     except ValueError:
         return False
     return True
@@ -48,7 +49,7 @@ def check_password(password, encoded, setter=None, preferred='default'):
     If setter is specified, it'll be called when you need to
     regenerate the password.
     """
-    if not is_password_usable(encoded):
+    if password is None or not is_password_usable(encoded):
         return False
 
     preferred = get_hasher(preferred)
diff --git a/django/contrib/auth/tests/test_hashers.py b/django/contrib/auth/tests/test_hashers.py
index 8e8119b741..4b90127c37 100644
--- a/django/contrib/auth/tests/test_hashers.py
+++ b/django/contrib/auth/tests/test_hashers.py
@@ -187,6 +187,13 @@ class TestUtilsHashPass(unittest.TestCase):
         # This might fail one day due to a hash collision.
         self.assertNotEqual(encoded, make_password(None), "Random password collision?")
 
+    def test_unspecified_password(self):
+        """
+        Makes sure specifying no plain password with a valid encoded password
+        returns `False`.
+        """
+        self.assertFalse(check_password(None, make_password('lètmein')))
+
     def test_bad_algorithm(self):
         with self.assertRaises(ValueError):
             make_password('lètmein', hasher='lolcat')
diff --git a/django/contrib/contenttypes/generic.py b/django/contrib/contenttypes/generic.py
index 04d4894b8a..6f120f82e0 100644
--- a/django/contrib/contenttypes/generic.py
+++ b/django/contrib/contenttypes/generic.py
@@ -66,7 +66,7 @@ class GenericForeignKey(six.with_metaclass(RenameGenericForeignKeyMethods)):
         if obj is not None:
             return ContentType.objects.db_manager(obj._state.db).get_for_model(
                 obj, for_concrete_model=self.for_concrete_model)
-        elif id:
+        elif id is not None:
             return ContentType.objects.db_manager(using).get_for_id(id)
         else:
             # This should never happen. I love comments like this, don't you?
@@ -130,7 +130,7 @@ class GenericForeignKey(six.with_metaclass(RenameGenericForeignKeyMethods)):
             # performance when dealing with GFKs in loops and such.
             f = self.model._meta.get_field(self.ct_field)
             ct_id = getattr(instance, f.get_attname(), None)
-            if ct_id:
+            if ct_id is not None:
                 ct = self.get_content_type(id=ct_id, using=instance._state.db)
                 try:
                     rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))
diff --git a/django/contrib/gis/db/backends/oracle/operations.py b/django/contrib/gis/db/backends/oracle/operations.py
index 84217c331b..628018320b 100644
--- a/django/contrib/gis/db/backends/oracle/operations.py
+++ b/django/contrib/gis/db/backends/oracle/operations.py
@@ -78,7 +78,7 @@ class OracleOperations(DatabaseOperations, BaseSpatialOperations):
 
     name = 'oracle'
     oracle = True
-    valid_aggregates = dict([(a, None) for a in ('Union', 'Extent')])
+    valid_aggregates = {'Union', 'Extent'}
 
     Adapter = OracleSpatialAdapter
     Adaptor = Adapter # Backwards-compatibility alias.
diff --git a/django/contrib/gis/db/backends/postgis/operations.py b/django/contrib/gis/db/backends/postgis/operations.py
index 84dbda3239..3863bea992 100644
--- a/django/contrib/gis/db/backends/postgis/operations.py
+++ b/django/contrib/gis/db/backends/postgis/operations.py
@@ -56,6 +56,7 @@ class PostGISSphereDistance(PostGISDistance):
 class PostGISRelate(PostGISFunctionParam):
     "For PostGIS Relate(<geom>, <pattern>) calls."
     pattern_regex = re.compile(r'^[012TF\*]{9}$')
+
     def __init__(self, prefix, pattern):
         if not self.pattern_regex.match(pattern):
             raise ValueError('Invalid intersection matrix pattern "%s".' % pattern)
@@ -68,8 +69,7 @@ class PostGISOperations(DatabaseOperations, BaseSpatialOperations):
     postgis = True
     geom_func_prefix = 'ST_'
     version_regex = re.compile(r'^(?P<major>\d)\.(?P<minor1>\d)\.(?P<minor2>\d+)')
-    valid_aggregates = dict([(k, None) for k in
-                             ('Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union')])
+    valid_aggregates = {'Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union'}
 
     Adapter = PostGISAdapter
     Adaptor = Adapter # Backwards-compatibility alias.
diff --git a/django/contrib/gis/db/backends/spatialite/operations.py b/django/contrib/gis/db/backends/spatialite/operations.py
index 4281cafa23..3cb2004dfd 100644
--- a/django/contrib/gis/db/backends/spatialite/operations.py
+++ b/django/contrib/gis/db/backends/spatialite/operations.py
@@ -56,7 +56,7 @@ class SpatiaLiteOperations(DatabaseOperations, BaseSpatialOperations):
     name = 'spatialite'
     spatialite = True
     version_regex = re.compile(r'^(?P<major>\d)\.(?P<minor1>\d)\.(?P<minor2>\d+)')
-    valid_aggregates = dict([(k, None) for k in ('Extent', 'Union')])
+    valid_aggregates = {'Extent', 'Union'}
 
     Adapter = SpatiaLiteAdapter
     Adaptor = Adapter # Backwards-compatibility alias.
@@ -169,6 +169,7 @@ class SpatiaLiteOperations(DatabaseOperations, BaseSpatialOperations):
         Checks if the given aggregate name is supported (that is, if it's
         in `self.valid_aggregates`).
         """
+        super(SpatiaLiteOperations, self).check_aggregate_support(aggregate)
         agg_name = aggregate.__class__.__name__
         return agg_name in self.valid_aggregates
 
diff --git a/django/contrib/gis/db/models/query.py b/django/contrib/gis/db/models/query.py
index c89912b2d9..4199d19a88 100644
--- a/django/contrib/gis/db/models/query.py
+++ b/django/contrib/gis/db/models/query.py
@@ -140,7 +140,7 @@ class GeoQuerySet(QuerySet):
         Returns a GeoJSON representation of the geomtry field in a `geojson`
         attribute on each element of the GeoQuerySet.
 
-        The `crs` and `bbox` keywords may be set to True if the users wants
+        The `crs` and `bbox` keywords may be set to True if the user wants
         the coordinate reference system and the bounding box to be included
         in the GeoJSON representation of the geometry.
         """
diff --git a/django/contrib/gis/gdal/geometries.py b/django/contrib/gis/gdal/geometries.py
index 0d75620b4e..d75e8cd288 100644
--- a/django/contrib/gis/gdal/geometries.py
+++ b/django/contrib/gis/gdal/geometries.py
@@ -198,14 +198,6 @@ class OGRGeometry(GDALBase):
 
     def _get_coord_dim(self):
         "Returns the coordinate dimension of the Geometry."
-        if isinstance(self, GeometryCollection) and GDAL_VERSION < (1, 5, 2):
-            # On GDAL versions prior to 1.5.2, there exists a bug in which
-            # the coordinate dimension of geometry collections is always 2:
-            #   http://trac.osgeo.org/gdal/ticket/2334
-            # Here we workaround by returning the coordinate dimension of the
-            # first geometry in the collection instead.
-            if len(self):
-                return capi.get_coord_dim(capi.get_geom_ref(self.ptr, 0))
         return capi.get_coord_dim(self.ptr)
 
     def _set_coord_dim(self, dim):
diff --git a/django/contrib/gis/management/commands/ogrinspect.py b/django/contrib/gis/management/commands/ogrinspect.py
index 44513e3463..2a29fe672a 100644
--- a/django/contrib/gis/management/commands/ogrinspect.py
+++ b/django/contrib/gis/management/commands/ogrinspect.py
@@ -53,7 +53,7 @@ class Command(LabelCommand):
         make_option('--multi-geom', action='store_true', dest='multi_geom', default=False,
                     help='Treat the geometry in the data source as a geometry collection.'),
         make_option('--name-field', dest='name_field',
-                    help='Specifies a field name to return for the `__unicode__` function.'),
+                    help='Specifies a field name to return for the `__unicode__`/`__str__` function.'),
         make_option('--no-imports', action='store_false', dest='imports', default=True,
                     help='Do not include `from django.contrib.gis.db import models` '
                     'statement.'),
diff --git a/django/contrib/gis/maps/google/gmap.py b/django/contrib/gis/maps/google/gmap.py
index 75b285ca76..ff6562696d 100644
--- a/django/contrib/gis/maps/google/gmap.py
+++ b/django/contrib/gis/maps/google/gmap.py
@@ -134,7 +134,8 @@ class GoogleMap(object):
     @property
     def scripts(self):
         "Returns all <script></script> tags required with Google Maps JavaScript."
-        return format_html('%s\n  <script type="text/javascript">\n//<![CDATA[\n%s//]]>\n  </script>', self.api_script, mark_safe(self.js))
+        return format_html('{0}\n  <script type="text/javascript">\n//<![CDATA[\n{1}//]]>\n  </script>',
+                           self.api_script, mark_safe(self.js))
 
     @property
     def style(self):
diff --git a/django/contrib/gis/tests/__init__.py b/django/contrib/gis/tests/__init__.py
index 1703f3f1b3..e69de29bb2 100644
--- a/django/contrib/gis/tests/__init__.py
+++ b/django/contrib/gis/tests/__init__.py
@@ -1,30 +0,0 @@
-def geo_apps():
-    """
-    Returns a list of GeoDjango test applications that reside in
-    `django.contrib.gis.tests` that can be used with the current
-    database and the spatial libraries that are installed.
-    """
-    from django.db import connection
-    from django.contrib.gis.geos import GEOS_PREPARE
-    from django.contrib.gis.gdal import HAS_GDAL
-
-    apps = ['geoapp', 'relatedapp']
-
-    # No distance queries on MySQL.
-    if not connection.ops.mysql:
-        apps.append('distapp')
-
-    # Test geography support with PostGIS 1.5+.
-    if connection.ops.postgis and connection.ops.geography:
-        apps.append('geogapp')
-
-    # The following GeoDjango test apps depend on GDAL support.
-    if HAS_GDAL:
-        # Geographic admin, LayerMapping, and ogrinspect test apps
-        # all require GDAL.
-        apps.extend(['geoadmin', 'layermap', 'inspectapp'])
-
-        # 3D apps use LayerMapping, which uses GDAL and require GEOS 3.1+.
-        if connection.ops.postgis and GEOS_PREPARE:
-            apps.append('geo3d')
-    return [('django.contrib.gis.tests', app) for app in apps]
diff --git a/django/contrib/gis/tests/geoadmin/tests.py b/django/contrib/gis/tests/geoadmin/tests.py
index c34964a2da..df4158bb31 100644
--- a/django/contrib/gis/tests/geoadmin/tests.py
+++ b/django/contrib/gis/tests/geoadmin/tests.py
@@ -2,9 +2,10 @@ from __future__ import absolute_import
 
 from unittest import skipUnless
 
-from django.test import TestCase
 from django.contrib.gis.geos import HAS_GEOS
 from django.contrib.gis.tests.utils import HAS_SPATIAL_DB
+from django.test import TestCase
+from django.test.utils import override_settings
 
 if HAS_GEOS and HAS_SPATIAL_DB:
     from django.contrib.gis import admin
@@ -12,6 +13,8 @@ if HAS_GEOS and HAS_SPATIAL_DB:
 
     from .models import City
 
+GOOGLE_MAPS_API_KEY = 'XXXX'
+
 
 @skipUnless(HAS_GEOS and HAS_SPATIAL_DB, "Geos and spatial db are required.")
 class GeoAdminTest(TestCase):
@@ -39,7 +42,9 @@ class GeoAdminTest(TestCase):
             result)
 
     def test_olwidget_has_changed(self):
-        """ Check that changes are accurately noticed by OpenLayersWidget. """
+        """
+        Check that changes are accurately noticed by OpenLayersWidget.
+        """
         geoadmin = admin.site._registry[City]
         form = geoadmin.get_changelist_form(None)()
         has_changed = form.fields['point']._has_changed
@@ -55,3 +60,15 @@ class GeoAdminTest(TestCase):
         self.assertFalse(has_changed(initial, data_same))
         self.assertFalse(has_changed(initial, data_almost_same))
         self.assertTrue(has_changed(initial, data_changed))
+
+    @override_settings(GOOGLE_MAPS_API_KEY=GOOGLE_MAPS_API_KEY)
+    def test_google_map_scripts(self):
+        """
+        Testing GoogleMap.scripts() output. See #20773.
+        """
+        from django.contrib.gis.maps.google.gmap import GoogleMap
+
+        google_map = GoogleMap()
+        scripts = google_map.scripts
+        self.assertIn(GOOGLE_MAPS_API_KEY, scripts)
+        self.assertIn("new GMap2", scripts)
diff --git a/django/contrib/gis/tests/geoapp/test_sitemaps.py b/django/contrib/gis/tests/geoapp/test_sitemaps.py
index facd94c247..98cd8cc5ac 100644
--- a/django/contrib/gis/tests/geoapp/test_sitemaps.py
+++ b/django/contrib/gis/tests/geoapp/test_sitemaps.py
@@ -3,6 +3,7 @@ from __future__ import absolute_import
 from io import BytesIO
 from unittest import skipUnless
 from xml.dom import minidom
+import os
 import zipfile
 
 from django.conf import settings
@@ -10,6 +11,7 @@ from django.contrib.gis.geos import HAS_GEOS
 from django.contrib.gis.tests.utils import HAS_SPATIAL_DB
 from django.contrib.sites.models import Site
 from django.test import TestCase
+from django.utils._os import upath
 
 if HAS_GEOS:
     from .models import City, Country
@@ -37,7 +39,11 @@ class GeoSitemapTest(TestCase):
     def test_geositemap_index(self):
         "Tests geographic sitemap index."
         # Getting the geo index.
-        doc = minidom.parseString(self.client.get('/sitemap.xml').content)
+        from django.contrib import sitemaps
+        template_dirs = settings.TEMPLATE_DIRS + (
+            os.path.join(os.path.dirname(upath(sitemaps.__file__)), 'templates'),)
+        with self.settings(TEMPLATE_DIRS=template_dirs):
+            doc = minidom.parseString(self.client.get('/sitemap.xml').content)
         index = doc.firstChild
         self.assertEqual(index.getAttribute('xmlns'), 'http://www.sitemaps.org/schemas/sitemap/0.9')
         self.assertEqual(3, len(index.getElementsByTagName('sitemap')))
diff --git a/django/contrib/gis/tests/geoapp/tests.py b/django/contrib/gis/tests/geoapp/tests.py
index 487f879674..eabc5958c0 100644
--- a/django/contrib/gis/tests/geoapp/tests.py
+++ b/django/contrib/gis/tests/geoapp/tests.py
@@ -8,7 +8,7 @@ from django.db import connection
 from django.contrib.gis import gdal
 from django.contrib.gis.geos import HAS_GEOS
 from django.contrib.gis.tests.utils import (
-    no_mysql, no_oracle, no_spatialite,
+    HAS_SPATIAL_DB, no_mysql, no_oracle, no_spatialite,
     mysql, oracle, postgis, spatialite)
 from django.test import TestCase
 from django.utils import six
@@ -28,7 +28,7 @@ def postgis_bug_version():
     return spatial_version and (2, 0, 0) <= spatial_version <= (2, 0, 1)
 
 
-@skipUnless(HAS_GEOS and postgis, "Geos and postgis are required.")
+@skipUnless(HAS_GEOS and HAS_SPATIAL_DB, "Geos and spatial db are required.")
 class GeoModelTest(TestCase):
 
     def test_fixtures(self):
@@ -203,7 +203,7 @@ class GeoModelTest(TestCase):
         self.assertTrue(isinstance(cities2[0].point, Point))
 
 
-@skipUnless(HAS_GEOS and postgis, "Geos and postgis are required.")
+@skipUnless(HAS_GEOS and HAS_SPATIAL_DB, "Geos and spatial db are required.")
 class GeoLookupTest(TestCase):
 
     @no_mysql
@@ -389,7 +389,7 @@ class GeoLookupTest(TestCase):
             self.assertEqual('Lawrence', City.objects.get(point__relate=(ks.poly, intersects_mask)).name)
 
 
-@skipUnless(HAS_GEOS and postgis, "Geos and postgis are required.")
+@skipUnless(HAS_GEOS and HAS_SPATIAL_DB, "Geos and spatial db are required.")
 class GeoQuerySetTest(TestCase):
     # Please keep the tests in GeoQuerySet method's alphabetic order
 
@@ -433,6 +433,13 @@ class GeoQuerySetTest(TestCase):
                 self.assertEqual(c.mpoly.sym_difference(geom), c.sym_difference)
                 self.assertEqual(c.mpoly.union(geom), c.union)
 
+    @skipUnless(getattr(connection.ops, 'envelope', False), 'Database does not support envelope operation')
+    def test_envelope(self):
+        "Testing the `envelope` GeoQuerySet method."
+        countries = Country.objects.all().envelope()
+        for country in countries:
+            self.assertIsInstance(country.envelope, Polygon)
+
     @no_mysql
     @no_spatialite # SpatiaLite does not have an Extent function
     def test_extent(self):
diff --git a/django/contrib/gis/tests/test_spatialrefsys.py b/django/contrib/gis/tests/test_spatialrefsys.py
index 8daa6acc23..5bb6a70206 100644
--- a/django/contrib/gis/tests/test_spatialrefsys.py
+++ b/django/contrib/gis/tests/test_spatialrefsys.py
@@ -23,7 +23,7 @@ test_srs = ({'srid' : 4326,
              'auth_srid' : 32140,
              'srtext' : 'PROJCS["NAD83 / Texas South Central",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS 1980"',
              'proj4_re' : r'\+proj=lcc \+lat_1=30.28333333333333 \+lat_2=28.38333333333333 \+lat_0=27.83333333333333 '
-                          r'\+lon_0=-99 \+x_0=600000 \+y_0=4000000 \+ellps=GRS80 '
+                          r'\+lon_0=-99 \+x_0=600000 \+y_0=4000000 (\+ellps=GRS80 )?'
                           r'(\+datum=NAD83 |\+towgs84=0,0,0,0,0,0,0)?\+units=m \+no_defs ',
              'spheroid' : 'GRS 1980', 'name' : 'NAD83 / Texas South Central',
              'geographic' : False, 'projected' : True, 'spatialite' : False,
diff --git a/django/contrib/gis/utils/ogrinspect.py b/django/contrib/gis/utils/ogrinspect.py
index 08d3b40397..b7cfafd49d 100644
--- a/django/contrib/gis/utils/ogrinspect.py
+++ b/django/contrib/gis/utils/ogrinspect.py
@@ -89,7 +89,7 @@ def ogrinspect(*args, **kwargs):
      `multi_geom` => Boolean (default: False) - specify as multigeometry.
 
      `name_field` => String - specifies a field name to return for the
-       `__unicode__` function (which will be generated if specified).
+       `__unicode__`/`__str__` function (which will be generated if specified).
 
      `imports` => Boolean (default: True) - set to False to omit the
        `from django.contrib.gis.db import models` code from the
@@ -221,4 +221,5 @@ def _ogrinspect(data_source, model_name, geom_name='geom', layer_key=0, srid=Non
 
     if name_field:
         yield ''
-        yield '    def __str__(self): return self.%s' % name_field
+        yield '    def __%s__(self): return self.%s' % (
+            'str' if six.PY3 else 'unicode', name_field)
diff --git a/django/contrib/syndication/views.py b/django/contrib/syndication/views.py
index 3bfba3ba08..cec204dc92 100644
--- a/django/contrib/syndication/views.py
+++ b/django/contrib/syndication/views.py
@@ -43,9 +43,9 @@ class Feed(object):
             raise Http404('Feed object does not exist.')
         feedgen = self.get_feed(obj, request)
         response = HttpResponse(content_type=feedgen.mime_type)
-        if hasattr(self, 'item_pubdate'):
-            # if item_pubdate is defined for the feed, set header so as
-            # ConditionalGetMiddleware is able to send 304 NOT MODIFIED
+        if hasattr(self, 'item_pubdate') or hasattr(self, 'item_updateddate'):
+            # if item_pubdate or item_updateddate is defined for the feed, set
+            # header so as ConditionalGetMiddleware is able to send 304 NOT MODIFIED
             response['Last-Modified'] = http_date(
                 timegm(feedgen.latest_post_date().utctimetuple()))
         feedgen.write(response, 'utf-8')
@@ -191,6 +191,11 @@ class Feed(object):
                 ltz = tzinfo.LocalTimezone(pubdate)
                 pubdate = pubdate.replace(tzinfo=ltz)
 
+            updateddate = self.__get_dynamic_attr('item_updateddate', item)
+            if updateddate and is_naive(updateddate):
+                ltz = tzinfo.LocalTimezone(updateddate)
+                updateddate = updateddate.replace(tzinfo=ltz)
+
             feed.add_item(
                 title = title,
                 link = link,
@@ -200,6 +205,7 @@ class Feed(object):
                     'item_guid_is_permalink', item),
                 enclosure = enc,
                 pubdate = pubdate,
+                updateddate = updateddate,
                 author_name = author_name,
                 author_email = author_email,
                 author_link = author_link,
diff --git a/django/core/cache/backends/locmem.py b/django/core/cache/backends/locmem.py
index 1fa17052fd..44d7db62c3 100644
--- a/django/core/cache/backends/locmem.py
+++ b/django/core/cache/backends/locmem.py
@@ -9,16 +9,17 @@ except ImportError:
 from django.core.cache.backends.base import BaseCache, DEFAULT_TIMEOUT
 from django.utils.synch import RWLock
 
+
 # Global in-memory store of cache data. Keyed by name, to provide
 # multiple named local memory caches.
 _caches = {}
 _expire_info = {}
 _locks = {}
 
+
 class LocMemCache(BaseCache):
     def __init__(self, name, params):
         BaseCache.__init__(self, params)
-        global _caches, _expire_info, _locks
         self._cache = _caches.setdefault(name, {})
         self._expire_info = _expire_info.setdefault(name, {})
         self._lock = _locks.setdefault(name, RWLock())
@@ -26,28 +27,31 @@ class LocMemCache(BaseCache):
     def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
+        try:
+            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+        except pickle.PickleError:
+            return False
         with self._lock.writer():
             exp = self._expire_info.get(key)
             if exp is None or exp <= time.time():
-                try:
-                    pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
-                    self._set(key, pickled, timeout)
-                    return True
-                except pickle.PickleError:
-                    pass
+                self._set(key, pickled, timeout)
+                return True
             return False
 
     def get(self, key, default=None, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
+        pickled = None
         with self._lock.reader():
             exp = self._expire_info.get(key, 0)
             if exp is None or exp > time.time():
-                try:
-                    pickled = self._cache[key]
-                    return pickle.loads(pickled)
-                except pickle.PickleError:
-                    return default
+                pickled = self._cache[key]
+        if pickled is not None:
+            try:
+                return pickle.loads(pickled)
+            except pickle.PickleError:
+                return default
+
         with self._lock.writer():
             try:
                 del self._cache[key]
@@ -68,12 +72,13 @@ class LocMemCache(BaseCache):
     def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
-        with self._lock.writer():
-            try:
-                pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+        try:
+            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+        except pickle.PickleError:
+            pass
+        else:
+            with self._lock.writer():
                 self._set(key, pickled, timeout)
-            except pickle.PickleError:
-                pass
 
     def incr(self, key, delta=1, version=None):
         value = self.get(key, version=version)
@@ -81,12 +86,13 @@ class LocMemCache(BaseCache):
             raise ValueError("Key '%s' not found" % key)
         new_value = value + delta
         key = self.make_key(key, version=version)
-        with self._lock.writer():
-            try:
-                pickled = pickle.dumps(new_value, pickle.HIGHEST_PROTOCOL)
+        try:
+            pickled = pickle.dumps(new_value, pickle.HIGHEST_PROTOCOL)
+        except pickle.PickleError:
+            pass
+        else:
+            with self._lock.writer():
                 self._cache[key] = pickled
-            except pickle.PickleError:
-                pass
         return new_value
 
     def has_key(self, key, version=None):
@@ -135,6 +141,7 @@ class LocMemCache(BaseCache):
         self._cache.clear()
         self._expire_info.clear()
 
+
 # For backwards compatibility
 class CacheClass(LocMemCache):
     pass
diff --git a/django/core/cache/backends/memcached.py b/django/core/cache/backends/memcached.py
index 64d1c41dc5..19e8b02f74 100644
--- a/django/core/cache/backends/memcached.py
+++ b/django/core/cache/backends/memcached.py
@@ -86,7 +86,7 @@ class BaseMemcachedCache(BaseCache):
         self._cache.delete(key)
 
     def get_many(self, keys, version=None):
-        new_keys = map(lambda x: self.make_key(x, version=version), keys)
+        new_keys = [self.make_key(x, version=version) for x in keys]
         ret = self._cache.get_multi(new_keys)
         if ret:
             _ = {}
diff --git a/django/core/files/uploadedfile.py b/django/core/files/uploadedfile.py
index 39b99ff78f..9f948ca03b 100644
--- a/django/core/files/uploadedfile.py
+++ b/django/core/files/uploadedfile.py
@@ -23,11 +23,12 @@ class UploadedFile(File):
     """
     DEFAULT_CHUNK_SIZE = 64 * 2**10
 
-    def __init__(self, file=None, name=None, content_type=None, size=None, charset=None):
+    def __init__(self, file=None, name=None, content_type=None, size=None, charset=None, content_type_extra=None):
         super(UploadedFile, self).__init__(file, name)
         self.size = size
         self.content_type = content_type
         self.charset = charset
+        self.content_type_extra = content_type_extra
 
     def __repr__(self):
         return force_str("<%s: %s (%s)>" % (
@@ -55,13 +56,13 @@ class TemporaryUploadedFile(UploadedFile):
     """
     A file uploaded to a temporary location (i.e. stream-to-disk).
     """
-    def __init__(self, name, content_type, size, charset):
+    def __init__(self, name, content_type, size, charset, content_type_extra):
         if settings.FILE_UPLOAD_TEMP_DIR:
             file = tempfile.NamedTemporaryFile(suffix='.upload',
                 dir=settings.FILE_UPLOAD_TEMP_DIR)
         else:
             file = tempfile.NamedTemporaryFile(suffix='.upload')
-        super(TemporaryUploadedFile, self).__init__(file, name, content_type, size, charset)
+        super(TemporaryUploadedFile, self).__init__(file, name, content_type, size, charset, content_type_extra)
 
     def temporary_file_path(self):
         """
@@ -83,8 +84,8 @@ class InMemoryUploadedFile(UploadedFile):
     """
     A file uploaded into memory (i.e. stream-to-memory).
     """
-    def __init__(self, file, field_name, name, content_type, size, charset):
-        super(InMemoryUploadedFile, self).__init__(file, name, content_type, size, charset)
+    def __init__(self, file, field_name, name, content_type, size, charset, content_type_extra):
+        super(InMemoryUploadedFile, self).__init__(file, name, content_type, size, charset, content_type_extra)
         self.field_name = field_name
 
     def open(self, mode=None):
@@ -109,7 +110,7 @@ class SimpleUploadedFile(InMemoryUploadedFile):
     def __init__(self, name, content, content_type='text/plain'):
         content = content or b''
         super(SimpleUploadedFile, self).__init__(BytesIO(content), None, name,
-                                                 content_type, len(content), None)
+                                                 content_type, len(content), None, None)
 
     def from_dict(cls, file_dict):
         """
diff --git a/django/core/files/uploadhandler.py b/django/core/files/uploadhandler.py
index f5e95cf2fd..6739b26e0c 100644
--- a/django/core/files/uploadhandler.py
+++ b/django/core/files/uploadhandler.py
@@ -64,6 +64,7 @@ class FileUploadHandler(object):
         self.content_type = None
         self.content_length = None
         self.charset = None
+        self.content_type_extra = None
         self.request = request
 
     def handle_raw_input(self, input_data, META, content_length, boundary, encoding=None):
@@ -84,7 +85,7 @@ class FileUploadHandler(object):
         """
         pass
 
-    def new_file(self, field_name, file_name, content_type, content_length, charset=None):
+    def new_file(self, field_name, file_name, content_type, content_length, charset=None, content_type_extra=None):
         """
         Signal that a new file has been started.
 
@@ -96,6 +97,7 @@ class FileUploadHandler(object):
         self.content_type = content_type
         self.content_length = content_length
         self.charset = charset
+        self.content_type_extra = content_type_extra
 
     def receive_data_chunk(self, raw_data, start):
         """
@@ -132,7 +134,7 @@ class TemporaryFileUploadHandler(FileUploadHandler):
         Create the file object to append to as data is coming in.
         """
         super(TemporaryFileUploadHandler, self).new_file(file_name, *args, **kwargs)
-        self.file = TemporaryUploadedFile(self.file_name, self.content_type, 0, self.charset)
+        self.file = TemporaryUploadedFile(self.file_name, self.content_type, 0, self.charset, self.content_type_extra)
 
     def receive_data_chunk(self, raw_data, start):
         self.file.write(raw_data)
@@ -187,7 +189,8 @@ class MemoryFileUploadHandler(FileUploadHandler):
             name = self.file_name,
             content_type = self.content_type,
             size = file_size,
-            charset = self.charset
+            charset = self.charset,
+            content_type_extra = self.content_type_extra
         )
 
 
diff --git a/django/core/mail/backends/console.py b/django/core/mail/backends/console.py
index ea0cb5d9ad..389e06b37f 100644
--- a/django/core/mail/backends/console.py
+++ b/django/core/mail/backends/console.py
@@ -16,6 +16,7 @@ class EmailBackend(BaseEmailBackend):
         """Write all messages to the stream in a thread-safe way."""
         if not email_messages:
             return
+        msg_count = 0
         with self._lock:
             try:
                 stream_created = self.open()
@@ -24,9 +25,10 @@ class EmailBackend(BaseEmailBackend):
                     self.stream.write('-' * 79)
                     self.stream.write('\n')
                     self.stream.flush()  # flush after each message
+                    msg_count += 1
                 if stream_created:
                     self.close()
             except:
                 if not self.fail_silently:
                     raise
-        return len(email_messages)
+        return msg_count
diff --git a/django/core/mail/backends/dummy.py b/django/core/mail/backends/dummy.py
index 273aa0d88e..7ae4878f13 100644
--- a/django/core/mail/backends/dummy.py
+++ b/django/core/mail/backends/dummy.py
@@ -6,4 +6,4 @@ from django.core.mail.backends.base import BaseEmailBackend
 
 class EmailBackend(BaseEmailBackend):
     def send_messages(self, email_messages):
-        return len(email_messages)
+        return len(list(email_messages))
diff --git a/django/core/mail/backends/locmem.py b/django/core/mail/backends/locmem.py
index 6826d09ee5..8e893af358 100644
--- a/django/core/mail/backends/locmem.py
+++ b/django/core/mail/backends/locmem.py
@@ -20,7 +20,9 @@ class EmailBackend(BaseEmailBackend):
 
     def send_messages(self, messages):
         """Redirect messages to the dummy outbox"""
+        msg_count = 0
         for message in messages:  # .message() triggers header validation
             message.message()
+            msg_count += 1
         mail.outbox.extend(messages)
-        return len(messages)
+        return msg_count
diff --git a/django/core/mail/backends/smtp.py b/django/core/mail/backends/smtp.py
index e456b7864e..c7f4a1a801 100644
--- a/django/core/mail/backends/smtp.py
+++ b/django/core/mail/backends/smtp.py
@@ -15,22 +15,18 @@ class EmailBackend(BaseEmailBackend):
     A wrapper that manages the SMTP network connection.
     """
     def __init__(self, host=None, port=None, username=None, password=None,
-                 use_tls=None, fail_silently=False, **kwargs):
+                 use_tls=None, fail_silently=False, use_ssl=None, **kwargs):
         super(EmailBackend, self).__init__(fail_silently=fail_silently)
         self.host = host or settings.EMAIL_HOST
         self.port = port or settings.EMAIL_PORT
-        if username is None:
-            self.username = settings.EMAIL_HOST_USER
-        else:
-            self.username = username
-        if password is None:
-            self.password = settings.EMAIL_HOST_PASSWORD
-        else:
-            self.password = password
-        if use_tls is None:
-            self.use_tls = settings.EMAIL_USE_TLS
-        else:
-            self.use_tls = use_tls
+        self.username = settings.EMAIL_HOST_USER if username is None else username
+        self.password = settings.EMAIL_HOST_PASSWORD if password is None else password
+        self.use_tls = settings.EMAIL_USE_TLS if use_tls is None else use_tls
+        self.use_ssl = settings.EMAIL_USE_SSL if use_ssl is None else use_ssl
+        if self.use_ssl and self.use_tls:
+            raise ValueError(
+                "EMAIL_USE_TLS/EMAIL_USE_SSL are mutually exclusive, so only set "
+                "one of those settings to True.")
         self.connection = None
         self._lock = threading.RLock()
 
@@ -45,12 +41,18 @@ class EmailBackend(BaseEmailBackend):
         try:
             # If local_hostname is not specified, socket.getfqdn() gets used.
             # For performance, we use the cached FQDN for local_hostname.
-            self.connection = smtplib.SMTP(self.host, self.port,
+            if self.use_ssl:
+                self.connection = smtplib.SMTP_SSL(self.host, self.port,
                                            local_hostname=DNS_NAME.get_fqdn())
-            if self.use_tls:
-                self.connection.ehlo()
-                self.connection.starttls()
-                self.connection.ehlo()
+            else:
+                self.connection = smtplib.SMTP(self.host, self.port,
+                                           local_hostname=DNS_NAME.get_fqdn())
+                # TLS/SSL are mutually exclusive, so only attempt TLS over
+                # non-secure connections.
+                if self.use_tls:
+                    self.connection.ehlo()
+                    self.connection.starttls()
+                    self.connection.ehlo()
             if self.username and self.password:
                 self.connection.login(self.username, self.password)
             return True
diff --git a/django/core/mail/message.py b/django/core/mail/message.py
index 98ab3c9075..db9023a0bb 100644
--- a/django/core/mail/message.py
+++ b/django/core/mail/message.py
@@ -3,7 +3,6 @@ from __future__ import unicode_literals
 import mimetypes
 import os
 import random
-import sys
 import time
 from email import charset as Charset, encoders as Encoders
 from email.generator import Generator
@@ -139,9 +138,6 @@ class SafeMIMEText(MIMEText):
         """
         fp = six.StringIO()
         g = Generator(fp, mangle_from_ = False)
-        if sys.version_info < (2, 6, 6) and isinstance(self._payload, six.text_type):
-            # Workaround for http://bugs.python.org/issue1368247
-            self._payload = self._payload.encode(self._charset.output_charset)
         g.flatten(self, unixfrom=unixfrom)
         return fp.getvalue()
 
diff --git a/django/core/signing.py b/django/core/signing.py
index bbe53aafe3..c3b2c3ed36 100644
--- a/django/core/signing.py
+++ b/django/core/signing.py
@@ -183,6 +183,10 @@ class TimestampSigner(Signer):
         return super(TimestampSigner, self).sign(value)
 
     def unsign(self, value, max_age=None):
+        """
+        Retrieve original value and check it wasn't signed more
+        than max_age seconds ago.
+        """
         result =  super(TimestampSigner, self).unsign(value)
         value, timestamp = result.rsplit(self.sep, 1)
         timestamp = baseconv.base62.decode(timestamp)
diff --git a/django/core/validators.py b/django/core/validators.py
index 200d28fe02..aa417ed099 100644
--- a/django/core/validators.py
+++ b/django/core/validators.py
@@ -87,7 +87,7 @@ class EmailValidator(object):
         r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*"$)', # quoted-string
         re.IGNORECASE)
     domain_regex = re.compile(
-        r'(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}\.?$)'  # domain
+        r'(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}|[A-Z0-9-]{2,})\.?$'  # domain
         # literal form, ipv4 address (SMTP 4.1.3)
         r'|^\[(25[0-5]|2[0-4]\d|[0-1]?\d?\d)(\.(25[0-5]|2[0-4]\d|[0-1]?\d?\d)){3}\]$',
         re.IGNORECASE)
diff --git a/django/db/__init__.py b/django/db/__init__.py
index 0d7fbe2a34..e1af430dc2 100644
--- a/django/db/__init__.py
+++ b/django/db/__init__.py
@@ -1,20 +1,25 @@
 import warnings
 
 from django.core import signals
-from django.db.utils import (DEFAULT_DB_ALIAS,
-    DataError, OperationalError, IntegrityError, InternalError,
-    ProgrammingError, NotSupportedError, DatabaseError,
-    InterfaceError, Error,
-    load_backend, ConnectionHandler, ConnectionRouter)
+from django.db.utils import (DEFAULT_DB_ALIAS, DataError, OperationalError,
+    IntegrityError, InternalError, ProgrammingError, NotSupportedError,
+    DatabaseError, InterfaceError, Error, load_backend,
+    ConnectionHandler, ConnectionRouter)
 from django.utils.functional import cached_property
 
-__all__ = ('backend', 'connection', 'connections', 'router', 'DatabaseError',
-    'IntegrityError', 'DEFAULT_DB_ALIAS')
+
+__all__ = [
+    'backend', 'connection', 'connections', 'router', 'DatabaseError',
+    'IntegrityError', 'InternalError', 'ProgrammingError', 'DataError',
+    'NotSupportedError', 'Error', 'InterfaceError', 'OperationalError',
+    'DEFAULT_DB_ALIAS'
+]
 
 connections = ConnectionHandler()
 
 router = ConnectionRouter()
 
+
 # `connection`, `DatabaseError` and `IntegrityError` are convenient aliases
 # for backend bits.
 
@@ -39,8 +44,15 @@ class DefaultConnectionProxy(object):
     def __delattr__(self, name):
         return delattr(connections[DEFAULT_DB_ALIAS], name)
 
+    def __eq__(self, other):
+        return connections[DEFAULT_DB_ALIAS] == other
+
+    def __ne__(self, other):
+        return connections[DEFAULT_DB_ALIAS] != other
+
 connection = DefaultConnectionProxy()
 
+
 class DefaultBackendProxy(object):
     """
     Temporary proxy class used during deprecation period of the `backend` module
@@ -63,6 +75,7 @@ class DefaultBackendProxy(object):
 
 backend = DefaultBackendProxy()
 
+
 def close_connection(**kwargs):
     warnings.warn(
         "close_connection is superseded by close_old_connections.",
@@ -76,12 +89,14 @@ def close_connection(**kwargs):
         transaction.abort(conn)
         connections[conn].close()
 
+
 # Register an event to reset saved queries when a Django request is started.
 def reset_queries(**kwargs):
     for conn in connections.all():
         conn.queries = []
 signals.request_started.connect(reset_queries)
 
+
 # Register an event to reset transaction state and close connections past
 # their lifetime. NB: abort() doesn't do anything outside of a transaction.
 def close_old_connections(**kwargs):
diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index 451cf4baf1..80e66b3ad4 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -70,7 +70,9 @@ class BaseDatabaseWrapper(object):
         self._thread_ident = thread.get_ident()
 
     def __eq__(self, other):
-        return self.alias == other.alias
+        if isinstance(other, BaseDatabaseWrapper):
+            return self.alias == other.alias
+        return NotImplemented
 
     def __ne__(self, other):
         return not self == other
@@ -1184,6 +1186,7 @@ FieldInfo = namedtuple('FieldInfo',
     'name type_code display_size internal_size precision scale null_ok'
 )
 
+
 class BaseDatabaseIntrospection(object):
     """
     This class encapsulates all backend-specific introspection utilities
diff --git a/django/db/backends/creation.py b/django/db/backends/creation.py
index 2767fcb48d..2ebbbbf2d5 100644
--- a/django/db/backends/creation.py
+++ b/django/db/backends/creation.py
@@ -253,12 +253,13 @@ class BaseDatabaseCreation(object):
             r_col = model._meta.get_field(f.rel.field_name).column
             r_name = '%s_refs_%s_%s' % (
                 col, r_col, self._digest(table, r_table))
-            output.append('%s %s %s %s;' % \
-                (style.SQL_KEYWORD('ALTER TABLE'),
+            output.append('%s %s %s %s;' % (
+                style.SQL_KEYWORD('ALTER TABLE'),
                 style.SQL_TABLE(qn(table)),
                 style.SQL_KEYWORD(self.connection.ops.drop_foreignkey_sql()),
                 style.SQL_FIELD(qn(truncate_name(
-                    r_name, self.connection.ops.max_name_length())))))
+                    r_name, self.connection.ops.max_name_length())))
+            ))
         del references_to_delete[model]
         return output
 
diff --git a/django/db/backends/dummy/base.py b/django/db/backends/dummy/base.py
index 9a220ffd8b..3e6d3e4c5a 100644
--- a/django/db/backends/dummy/base.py
+++ b/django/db/backends/dummy/base.py
@@ -8,33 +8,43 @@ ImproperlyConfigured.
 """
 
 from django.core.exceptions import ImproperlyConfigured
-from django.db.backends import *
+from django.db.backends import (BaseDatabaseOperations, BaseDatabaseClient,
+    BaseDatabaseIntrospection, BaseDatabaseWrapper, BaseDatabaseFeatures,
+    BaseDatabaseValidation)
 from django.db.backends.creation import BaseDatabaseCreation
 
+
 def complain(*args, **kwargs):
     raise ImproperlyConfigured("settings.DATABASES is improperly configured. "
                                "Please supply the ENGINE value. Check "
                                "settings documentation for more details.")
 
+
 def ignore(*args, **kwargs):
     pass
 
+
 class DatabaseError(Exception):
     pass
 
+
 class IntegrityError(DatabaseError):
     pass
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     quote_name = complain
 
+
 class DatabaseClient(BaseDatabaseClient):
     runshell = complain
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     create_test_db = ignore
     destroy_test_db = ignore
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     get_table_list = complain
     get_table_description = complain
@@ -42,6 +52,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
     get_indexes = complain
     get_key_columns = complain
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     operators = {}
     # Override the base class implementations with null
diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index 8a689f66ed..15eacec679 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -37,7 +37,8 @@ except ImportError:
 
 from django.conf import settings
 from django.db import utils
-from django.db.backends import *
+from django.db.backends import (util, BaseDatabaseFeatures,
+    BaseDatabaseOperations, BaseDatabaseWrapper)
 from django.db.backends.mysql.client import DatabaseClient
 from django.db.backends.mysql.creation import DatabaseCreation
 from django.db.backends.mysql.introspection import DatabaseIntrospection
@@ -60,6 +61,7 @@ IntegrityError = Database.IntegrityError
 # It's impossible to import datetime_or_None directly from MySQLdb.times
 parse_datetime = conversions[FIELD_TYPE.DATETIME]
 
+
 def parse_datetime_with_timezone_support(value):
     dt = parse_datetime(value)
     # Confirm that dt is naive before overwriting its tzinfo.
@@ -67,6 +69,7 @@ def parse_datetime_with_timezone_support(value):
         dt = dt.replace(tzinfo=timezone.utc)
     return dt
 
+
 def adapt_datetime_with_timezone_support(value, conv):
     # Equivalent to DateTimeField.get_db_prep_value. Used only by raw SQL.
     if settings.USE_TZ:
@@ -101,6 +104,7 @@ django_conversions.update({
 # http://dev.mysql.com/doc/refman/5.0/en/news.html .
 server_version_re = re.compile(r'(\d{1,2})\.(\d{1,2})\.(\d{1,2})')
 
+
 # MySQLdb-1.2.1 and newer automatically makes use of SHOW WARNINGS on
 # MySQL-4.1 and newer, so the MysqlDebugWrapper is unnecessary. Since the
 # point is to raise Warnings as exceptions, this can be done with the Python
@@ -151,6 +155,7 @@ class CursorWrapper(object):
     def __iter__(self):
         return iter(self.cursor)
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     empty_fetchmany_value = ()
     update_can_self_select = False
@@ -208,6 +213,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         cursor.execute("SELECT 1 FROM mysql.time_zone LIMIT 1")
         return cursor.fetchone() is not None
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.mysql.compiler"
 
@@ -323,7 +329,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         # Truncate already resets the AUTO_INCREMENT field from
         # MySQL version 5.0.13 onwards. Refs #16961.
         if self.connection.mysql_version < (5, 0, 13):
-            return ["%s %s %s %s %s;" % \
+            return ["%s %s %s %s %s;" %
                     (style.SQL_KEYWORD('ALTER'),
                     style.SQL_KEYWORD('TABLE'),
                     style.SQL_TABLE(self.quote_name(sequence['table'])),
@@ -377,6 +383,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         items_sql = "(%s)" % ", ".join(["%s"] * len(fields))
         return "VALUES " + ", ".join([items_sql] * num_values)
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'mysql'
     operators = {
diff --git a/django/db/backends/mysql/client.py b/django/db/backends/mysql/client.py
index 1cf8ceef9c..8364c7b6e6 100644
--- a/django/db/backends/mysql/client.py
+++ b/django/db/backends/mysql/client.py
@@ -3,6 +3,7 @@ import sys
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'mysql'
 
@@ -37,4 +38,3 @@ class DatabaseClient(BaseDatabaseClient):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/mysql/compiler.py b/django/db/backends/mysql/compiler.py
index 4e033e3d93..b7d1d7b98d 100644
--- a/django/db/backends/mysql/compiler.py
+++ b/django/db/backends/mysql/compiler.py
@@ -22,20 +22,26 @@ class SQLCompiler(compiler.SQLCompiler):
         sql, params = self.as_sql()
         return '(%s) IN (%s)' % (', '.join(['%s.%s' % (qn(alias), qn2(column)) for column in columns]), sql), params
 
+
 class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
     pass
 
+
 class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
     pass
 
+
 class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):
     pass
 
+
 class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateCompiler(compiler.SQLDateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateTimeCompiler(compiler.SQLDateTimeCompiler, SQLCompiler):
     pass
diff --git a/django/db/backends/mysql/creation.py b/django/db/backends/mysql/creation.py
index 3a57c29479..b59b225f4f 100644
--- a/django/db/backends/mysql/creation.py
+++ b/django/db/backends/mysql/creation.py
@@ -1,34 +1,35 @@
 from django.db.backends.creation import BaseDatabaseCreation
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # This dictionary maps Field objects to their associated MySQL column
     # types, as strings. Column-type strings can contain format strings; they'll
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
     data_types = {
-        'AutoField':         'integer AUTO_INCREMENT',
-        'BinaryField':       'longblob',
-        'BooleanField':      'bool',
-        'CharField':         'varchar(%(max_length)s)',
+        'AutoField': 'integer AUTO_INCREMENT',
+        'BinaryField': 'longblob',
+        'BooleanField': 'bool',
+        'CharField': 'varchar(%(max_length)s)',
         'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
-        'DateField':         'date',
-        'DateTimeField':     'datetime',
-        'DecimalField':      'numeric(%(max_digits)s, %(decimal_places)s)',
-        'FileField':         'varchar(%(max_length)s)',
-        'FilePathField':     'varchar(%(max_length)s)',
-        'FloatField':        'double precision',
-        'IntegerField':      'integer',
-        'BigIntegerField':   'bigint',
-        'IPAddressField':    'char(15)',
+        'DateField': 'date',
+        'DateTimeField': 'datetime',
+        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'double precision',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'char(15)',
         'GenericIPAddressField': 'char(39)',
-        'NullBooleanField':  'bool',
-        'OneToOneField':     'integer',
+        'NullBooleanField': 'bool',
+        'OneToOneField': 'integer',
         'PositiveIntegerField': 'integer UNSIGNED',
         'PositiveSmallIntegerField': 'smallint UNSIGNED',
-        'SlugField':         'varchar(%(max_length)s)',
+        'SlugField': 'varchar(%(max_length)s)',
         'SmallIntegerField': 'smallint',
-        'TextField':         'longtext',
-        'TimeField':         'time',
+        'TextField': 'longtext',
+        'TimeField': 'time',
     }
 
     def sql_table_creation_suffix(self):
diff --git a/django/db/backends/mysql/introspection.py b/django/db/backends/mysql/introspection.py
index 00c567a90b..e2d382b895 100644
--- a/django/db/backends/mysql/introspection.py
+++ b/django/db/backends/mysql/introspection.py
@@ -7,6 +7,7 @@ from django.utils.encoding import force_text
 
 foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     data_types_reverse = {
         FIELD_TYPE.BLOB: 'TextField',
diff --git a/django/db/backends/mysql/validation.py b/django/db/backends/mysql/validation.py
index 2ce957cce7..17b7cde756 100644
--- a/django/db/backends/mysql/validation.py
+++ b/django/db/backends/mysql/validation.py
@@ -1,5 +1,6 @@
 from django.db.backends import BaseDatabaseValidation
 
+
 class DatabaseValidation(BaseDatabaseValidation):
     def validate_field(self, errors, opts, f):
         """
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 5fb806807d..63d38bdafd 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -7,11 +7,12 @@ from __future__ import unicode_literals
 
 import decimal
 import re
+import platform
 import sys
 import warnings
 
+
 def _setup_environment(environ):
-    import platform
     # Cygwin requires some special voodoo to set the environment variables
     # properly so that Oracle will see them.
     if platform.system().upper().startswith('CYGWIN'):
@@ -91,6 +92,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_tablespaces = True
     supports_sequence_reset = False
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.oracle.compiler"
 
@@ -268,7 +270,7 @@ WHEN (new.%(col_name)s IS NULL)
         # http://cx-oracle.sourceforge.net/html/cursor.html#Cursor.statement
         # The DB API definition does not define this attribute.
         statement = cursor.statement
-        if not six.PY3 and not isinstance(statement, unicode):
+        if statement and not six.PY3 and not isinstance(statement, unicode):
             statement = statement.decode('utf-8')
         # Unlike Psycopg's `query` and MySQLdb`'s `_last_executed`, CxOracle's
         # `statement` doesn't contain the query parameters. refs #20010.
@@ -309,7 +311,7 @@ WHEN (new.%(col_name)s IS NULL)
         # Oracle puts the query text into a (query % args) construct, so % signs
         # in names need to be escaped. The '%%' will be collapsed back to '%' at
         # that stage so we aren't really making the name longer here.
-        name = name.replace('%','%%')
+        name = name.replace('%', '%%')
         return name.upper()
 
     def random_function_sql(self):
@@ -763,7 +765,7 @@ class FormatStylePlaceholderCursor(object):
 
     def _format_params(self, params):
         try:
-            return dict((k,OracleParam(v, self, True)) for k,v in params.items())
+            return dict((k, OracleParam(v, self, True)) for k, v in params.items())
         except AttributeError:
             return tuple([OracleParam(p, self, True) for p in params])
 
@@ -783,12 +785,12 @@ class FormatStylePlaceholderCursor(object):
                 for i, value in enumerate(params):
                     if value.input_size:
                         sizes[i] = value.input_size
-            self.setinputsizes(*sizes)        
+            self.setinputsizes(*sizes)
 
     def _param_generator(self, params):
         # Try dict handling; if that fails, treat as sequence
         if hasattr(params, 'items'):
-            return dict((k, v.force_bytes) for k,v in params.items())
+            return dict((k, v.force_bytes) for k, v in params.items())
         else:
             return [p.force_bytes for p in params]
 
@@ -804,14 +806,14 @@ class FormatStylePlaceholderCursor(object):
             query = convert_unicode(query, self.charset)
         elif hasattr(params, 'keys'):
             # Handle params as dict
-            args = dict((k, ":%s"%k) for k in params.keys())
+            args = dict((k, ":%s" % k) for k in params.keys())
             query = convert_unicode(query % args, self.charset)
         else:
             # Handle params as sequence
             args = [(':arg%d' % i) for i in range(len(params))]
             query = convert_unicode(query % tuple(args), self.charset)
         return query, self._format_params(params)
-        
+
     def execute(self, query, params=None):
         query, params = self._fix_for_params(query, params)
         self._guess_input_sizes([params])
@@ -830,9 +832,9 @@ class FormatStylePlaceholderCursor(object):
         # uniform treatment for sequences and iterables
         params_iter = iter(params)
         query, firstparams = self._fix_for_params(query, next(params_iter))
-        # we build a list of formatted params; as we're going to traverse it 
+        # we build a list of formatted params; as we're going to traverse it
         # more than once, we can't make it lazy by using a generator
-        formatted = [firstparams]+[self._format_params(p) for p in params_iter]
+        formatted = [firstparams] + [self._format_params(p) for p in params_iter]
         self._guess_input_sizes(formatted)
         try:
             return self.cursor.executemany(query,
diff --git a/django/db/backends/oracle/client.py b/django/db/backends/oracle/client.py
index ccc64ebffc..ac6b79041f 100644
--- a/django/db/backends/oracle/client.py
+++ b/django/db/backends/oracle/client.py
@@ -3,6 +3,7 @@ import sys
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'sqlplus'
 
@@ -13,4 +14,3 @@ class DatabaseClient(BaseDatabaseClient):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/oracle/compiler.py b/django/db/backends/oracle/compiler.py
index cbee27951c..d2d4cd3ac9 100644
--- a/django/db/backends/oracle/compiler.py
+++ b/django/db/backends/oracle/compiler.py
@@ -60,17 +60,22 @@ class SQLCompiler(compiler.SQLCompiler):
 class SQLInsertCompiler(compiler.SQLInsertCompiler, SQLCompiler):
     pass
 
+
 class SQLDeleteCompiler(compiler.SQLDeleteCompiler, SQLCompiler):
     pass
 
+
 class SQLUpdateCompiler(compiler.SQLUpdateCompiler, SQLCompiler):
     pass
 
+
 class SQLAggregateCompiler(compiler.SQLAggregateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateCompiler(compiler.SQLDateCompiler, SQLCompiler):
     pass
 
+
 class SQLDateTimeCompiler(compiler.SQLDateTimeCompiler, SQLCompiler):
     pass
diff --git a/django/db/backends/oracle/creation.py b/django/db/backends/oracle/creation.py
index 7f1192ed8a..f7d43ae7b6 100644
--- a/django/db/backends/oracle/creation.py
+++ b/django/db/backends/oracle/creation.py
@@ -5,9 +5,11 @@ from django.conf import settings
 from django.db.backends.creation import BaseDatabaseCreation
 from django.utils.six.moves import input
 
+
 TEST_DATABASE_PREFIX = 'test_'
 PASSWORD = 'Im_a_lumberjack'
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # This dictionary maps Field objects to their associated Oracle column
     # types, as strings. Column-type strings can contain format strings; they'll
@@ -18,30 +20,30 @@ class DatabaseCreation(BaseDatabaseCreation):
     # output (the "qn_" prefix is stripped before the lookup is performed.
 
     data_types = {
-        'AutoField':                    'NUMBER(11)',
-        'BinaryField':                  'BLOB',
-        'BooleanField':                 'NUMBER(1)',
-        'CharField':                    'NVARCHAR2(%(max_length)s)',
-        'CommaSeparatedIntegerField':   'VARCHAR2(%(max_length)s)',
-        'DateField':                    'DATE',
-        'DateTimeField':                'TIMESTAMP',
-        'DecimalField':                 'NUMBER(%(max_digits)s, %(decimal_places)s)',
-        'FileField':                    'NVARCHAR2(%(max_length)s)',
-        'FilePathField':                'NVARCHAR2(%(max_length)s)',
-        'FloatField':                   'DOUBLE PRECISION',
-        'IntegerField':                 'NUMBER(11)',
-        'BigIntegerField':              'NUMBER(19)',
-        'IPAddressField':               'VARCHAR2(15)',
-        'GenericIPAddressField':        'VARCHAR2(39)',
-        'NullBooleanField':             'NUMBER(1)',
-        'OneToOneField':                'NUMBER(11)',
-        'PositiveIntegerField':         'NUMBER(11)',
-        'PositiveSmallIntegerField':    'NUMBER(11)',
-        'SlugField':                    'NVARCHAR2(%(max_length)s)',
-        'SmallIntegerField':            'NUMBER(11)',
-        'TextField':                    'NCLOB',
-        'TimeField':                    'TIMESTAMP',
-        'URLField':                     'VARCHAR2(%(max_length)s)',
+        'AutoField': 'NUMBER(11)',
+        'BinaryField': 'BLOB',
+        'BooleanField': 'NUMBER(1)',
+        'CharField': 'NVARCHAR2(%(max_length)s)',
+        'CommaSeparatedIntegerField': 'VARCHAR2(%(max_length)s)',
+        'DateField': 'DATE',
+        'DateTimeField': 'TIMESTAMP',
+        'DecimalField': 'NUMBER(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'NVARCHAR2(%(max_length)s)',
+        'FilePathField': 'NVARCHAR2(%(max_length)s)',
+        'FloatField': 'DOUBLE PRECISION',
+        'IntegerField': 'NUMBER(11)',
+        'BigIntegerField': 'NUMBER(19)',
+        'IPAddressField': 'VARCHAR2(15)',
+        'GenericIPAddressField': 'VARCHAR2(39)',
+        'NullBooleanField': 'NUMBER(1)',
+        'OneToOneField': 'NUMBER(11)',
+        'PositiveIntegerField': 'NUMBER(11)',
+        'PositiveSmallIntegerField': 'NUMBER(11)',
+        'SlugField': 'NVARCHAR2(%(max_length)s)',
+        'SmallIntegerField': 'NUMBER(11)',
+        'TextField': 'NCLOB',
+        'TimeField': 'TIMESTAMP',
+        'URLField': 'VARCHAR2(%(max_length)s)',
     }
 
     data_type_check_constraints = {
@@ -190,7 +192,7 @@ class DatabaseCreation(BaseDatabaseCreation):
         statements = [
             'DROP TABLESPACE %(tblspace)s INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS',
             'DROP TABLESPACE %(tblspace_temp)s INCLUDING CONTENTS AND DATAFILES CASCADE CONSTRAINTS',
-            ]
+        ]
         self._execute_statements(cursor, statements, parameters, verbosity)
 
     def _destroy_test_user(self, cursor, parameters, verbosity):
diff --git a/django/db/backends/oracle/introspection.py b/django/db/backends/oracle/introspection.py
index 361308a62c..a2fad92509 100644
--- a/django/db/backends/oracle/introspection.py
+++ b/django/db/backends/oracle/introspection.py
@@ -1,10 +1,13 @@
+import re
+
+import cx_Oracle
+
 from django.db.backends import BaseDatabaseIntrospection, FieldInfo
 from django.utils.encoding import force_text
-import cx_Oracle
-import re
 
 foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     # Maps type objects to Django Field types.
     data_types_reverse = {
@@ -95,11 +98,11 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             SELECT ccol.column_name, rcol.table_name AS referenced_table, rcol.column_name AS referenced_column
             FROM user_constraints c
             JOIN user_cons_columns ccol
-              ON ccol.constraint_name = c.constraint_name 
+              ON ccol.constraint_name = c.constraint_name
             JOIN user_cons_columns rcol
-              ON rcol.constraint_name = c.r_constraint_name 
-            WHERE c.table_name = %s AND c.constraint_type = 'R'""" , [table_name.upper()])
-        return [tuple(cell.lower() for cell in row) 
+              ON rcol.constraint_name = c.r_constraint_name
+            WHERE c.table_name = %s AND c.constraint_type = 'R'""", [table_name.upper()])
+        return [tuple(cell.lower() for cell in row)
                 for row in cursor.fetchall()]
 
     def get_indexes(self, cursor, table_name):
diff --git a/django/db/backends/postgresql_psycopg2/base.py b/django/db/backends/postgresql_psycopg2/base.py
index bf75459b4a..f283476429 100644
--- a/django/db/backends/postgresql_psycopg2/base.py
+++ b/django/db/backends/postgresql_psycopg2/base.py
@@ -6,7 +6,9 @@ Requires psycopg 2: http://initd.org/projects/psycopg2
 import logging
 import sys
 
-from django.db.backends import *
+from django.conf import settings
+from django.db.backends import (BaseDatabaseFeatures, BaseDatabaseWrapper,
+    BaseDatabaseValidation)
 from django.db.backends.postgresql_psycopg2.operations import DatabaseOperations
 from django.db.backends.postgresql_psycopg2.client import DatabaseClient
 from django.db.backends.postgresql_psycopg2.creation import DatabaseCreation
@@ -34,11 +36,13 @@ psycopg2.extensions.register_adapter(SafeText, psycopg2.extensions.QuotedString)
 
 logger = logging.getLogger('django.db.backends')
 
+
 def utc_tzinfo_factory(offset):
     if offset != 0:
         raise AssertionError("database connection isn't set to UTC")
     return utc
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     needs_datetime_string_cast = False
     can_return_id_from_insert = True
@@ -55,6 +59,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_rollback_ddl = True
     supports_combined_alters = True
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'postgresql'
     operators = {
@@ -135,7 +140,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                 # Set the time zone in autocommit mode (see #17062)
                 self.set_autocommit(True)
                 self.connection.cursor().execute(
-                        self.ops.set_time_zone_sql(), [tz])
+                    self.ops.set_time_zone_sql(), [tz]
+                )
         self.connection.set_isolation_level(self.isolation_level)
 
     def create_cursor(self):
diff --git a/django/db/backends/postgresql_psycopg2/client.py b/django/db/backends/postgresql_psycopg2/client.py
index a5c02969ea..23ac9f2975 100644
--- a/django/db/backends/postgresql_psycopg2/client.py
+++ b/django/db/backends/postgresql_psycopg2/client.py
@@ -3,6 +3,7 @@ import sys
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'psql'
 
@@ -20,4 +21,3 @@ class DatabaseClient(BaseDatabaseClient):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/postgresql_psycopg2/creation.py b/django/db/backends/postgresql_psycopg2/creation.py
index 1bfda6354d..954e198764 100644
--- a/django/db/backends/postgresql_psycopg2/creation.py
+++ b/django/db/backends/postgresql_psycopg2/creation.py
@@ -8,29 +8,29 @@ class DatabaseCreation(BaseDatabaseCreation):
     # be interpolated against the values of Field.__dict__ before being output.
     # If a column type is set to None, it won't be included in the output.
     data_types = {
-        'AutoField':         'serial',
-        'BinaryField':       'bytea',
-        'BooleanField':      'boolean',
-        'CharField':         'varchar(%(max_length)s)',
+        'AutoField': 'serial',
+        'BinaryField': 'bytea',
+        'BooleanField': 'boolean',
+        'CharField': 'varchar(%(max_length)s)',
         'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
-        'DateField':         'date',
-        'DateTimeField':     'timestamp with time zone',
-        'DecimalField':      'numeric(%(max_digits)s, %(decimal_places)s)',
-        'FileField':         'varchar(%(max_length)s)',
-        'FilePathField':     'varchar(%(max_length)s)',
-        'FloatField':        'double precision',
-        'IntegerField':      'integer',
-        'BigIntegerField':   'bigint',
-        'IPAddressField':    'inet',
+        'DateField': 'date',
+        'DateTimeField': 'timestamp with time zone',
+        'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'double precision',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'inet',
         'GenericIPAddressField': 'inet',
-        'NullBooleanField':  'boolean',
-        'OneToOneField':     'integer',
+        'NullBooleanField': 'boolean',
+        'OneToOneField': 'integer',
         'PositiveIntegerField': 'integer',
         'PositiveSmallIntegerField': 'smallint',
-        'SlugField':         'varchar(%(max_length)s)',
+        'SlugField': 'varchar(%(max_length)s)',
         'SmallIntegerField': 'smallint',
-        'TextField':         'text',
-        'TimeField':         'time',
+        'TextField': 'text',
+        'TimeField': 'time',
     }
 
     data_type_check_constraints = {
@@ -59,7 +59,7 @@ class DatabaseCreation(BaseDatabaseCreation):
 
             def get_index_sql(index_name, opclass=''):
                 return (style.SQL_KEYWORD('CREATE INDEX') + ' ' +
-                        style.SQL_TABLE(qn(truncate_name(index_name,self.connection.ops.max_name_length()))) + ' ' +
+                        style.SQL_TABLE(qn(truncate_name(index_name, self.connection.ops.max_name_length()))) + ' ' +
                         style.SQL_KEYWORD('ON') + ' ' +
                         style.SQL_TABLE(qn(db_table)) + ' ' +
                         "(%s%s)" % (style.SQL_FIELD(qn(f.column)), opclass) +
diff --git a/django/db/backends/postgresql_psycopg2/introspection.py b/django/db/backends/postgresql_psycopg2/introspection.py
index 4f77059376..a816bb34d8 100644
--- a/django/db/backends/postgresql_psycopg2/introspection.py
+++ b/django/db/backends/postgresql_psycopg2/introspection.py
@@ -25,7 +25,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         1266: 'TimeField',
         1700: 'DecimalField',
     }
-        
+
     def get_table_list(self, cursor):
         "Returns a list of table names in the current database."
         cursor.execute("""
@@ -47,7 +47,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             WHERE table_name = %s""", [table_name])
         null_map = dict(cursor.fetchall())
         cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
-        return [FieldInfo(*((force_text(line[0]),) + line[1:6] + (null_map[force_text(line[0])]=='YES',)))
+        return [FieldInfo(*((force_text(line[0]),) + line[1:6] + (null_map[force_text(line[0])] == 'YES',)))
                 for line in cursor.description]
 
     def get_relations(self, cursor, table_name):
@@ -81,7 +81,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 ON ccu.constraint_catalog = tc.constraint_catalog
                     AND ccu.constraint_schema = tc.constraint_schema
                     AND ccu.constraint_name = tc.constraint_name
-            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""" , [table_name])
+            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""", [table_name])
         key_columns.extend(cursor.fetchall())
         return key_columns
 
diff --git a/django/db/backends/postgresql_psycopg2/operations.py b/django/db/backends/postgresql_psycopg2/operations.py
index c5aab84693..cc78ffe449 100644
--- a/django/db/backends/postgresql_psycopg2/operations.py
+++ b/django/db/backends/postgresql_psycopg2/operations.py
@@ -135,7 +135,7 @@ class DatabaseOperations(BaseDatabaseOperations):
                 # This will be the case if it's an m2m using an autogenerated
                 # intermediate table (see BaseDatabaseIntrospection.sequence_list)
                 column_name = 'id'
-            sql.append("%s setval(pg_get_serial_sequence('%s','%s'), 1, false);" % \
+            sql.append("%s setval(pg_get_serial_sequence('%s','%s'), 1, false);" %
                 (style.SQL_KEYWORD('SELECT'),
                 style.SQL_TABLE(self.quote_name(table_name)),
                 style.SQL_FIELD(column_name))
@@ -161,7 +161,7 @@ class DatabaseOperations(BaseDatabaseOperations):
 
             for f in model._meta.local_fields:
                 if isinstance(f, models.AutoField):
-                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \
+                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
                         (style.SQL_KEYWORD('SELECT'),
                         style.SQL_TABLE(qn(model._meta.db_table)),
                         style.SQL_FIELD(f.column),
@@ -173,7 +173,7 @@ class DatabaseOperations(BaseDatabaseOperations):
                     break # Only one AutoField is allowed per model, so don't bother continuing.
             for f in model._meta.many_to_many:
                 if not f.rel.through:
-                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" % \
+                    output.append("%s setval(pg_get_serial_sequence('%s','%s'), coalesce(max(%s), 1), max(%s) %s null) %s %s;" %
                         (style.SQL_KEYWORD('SELECT'),
                         style.SQL_TABLE(qn(f.m2m_db_table())),
                         style.SQL_FIELD('id'),
diff --git a/django/db/backends/postgresql_psycopg2/version.py b/django/db/backends/postgresql_psycopg2/version.py
index 8ef516704e..dae94f2dac 100644
--- a/django/db/backends/postgresql_psycopg2/version.py
+++ b/django/db/backends/postgresql_psycopg2/version.py
@@ -19,7 +19,8 @@ def _parse_version(text):
     try:
         return int(major) * 10000 + int(major2) * 100 + int(minor)
     except (ValueError, TypeError):
-        return int(major) * 10000 +  int(major2) * 100
+        return int(major) * 10000 + int(major2) * 100
+
 
 def get_version(connection):
     """
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index e330082108..960b6def03 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -11,8 +11,10 @@ import decimal
 import warnings
 import re
 
+from django.conf import settings
 from django.db import utils
-from django.db.backends import *
+from django.db.backends import (util, BaseDatabaseFeatures,
+    BaseDatabaseOperations, BaseDatabaseWrapper, BaseDatabaseValidation)
 from django.db.backends.sqlite3.client import DatabaseClient
 from django.db.backends.sqlite3.creation import DatabaseCreation
 from django.db.backends.sqlite3.introspection import DatabaseIntrospection
@@ -43,6 +45,7 @@ except ImportError:
 DatabaseError = Database.DatabaseError
 IntegrityError = Database.IntegrityError
 
+
 def parse_datetime_with_timezone_support(value):
     dt = parse_datetime(value)
     # Confirm that dt is naive before overwriting its tzinfo.
@@ -50,6 +53,7 @@ def parse_datetime_with_timezone_support(value):
         dt = dt.replace(tzinfo=timezone.utc)
     return dt
 
+
 def adapt_datetime_with_timezone_support(value):
     # Equivalent to DateTimeField.get_db_prep_value. Used only by raw SQL.
     if settings.USE_TZ:
@@ -62,6 +66,7 @@ def adapt_datetime_with_timezone_support(value):
         value = value.astimezone(timezone.utc).replace(tzinfo=None)
     return value.isoformat(str(" "))
 
+
 def decoder(conv_func):
     """ The Python sqlite3 interface returns always byte strings.
         This function converts the received value to a regular string before
@@ -82,6 +87,7 @@ Database.register_adapter(decimal.Decimal, util.rev_typecast_decimal)
 Database.register_adapter(str, lambda s: s.decode('utf-8'))
 Database.register_adapter(SafeBytes, lambda s: s.decode('utf-8'))
 
+
 class DatabaseFeatures(BaseDatabaseFeatures):
     # SQLite cannot handle us only partially reading from a cursor's result set
     # and then writing the same rows to the database in another cursor. This
@@ -127,6 +133,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     def has_zoneinfo_database(self):
         return pytz is not None
 
+
 class DatabaseOperations(BaseDatabaseOperations):
     def bulk_batch_size(self, fields, objs):
         """
@@ -275,6 +282,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         res.extend(["UNION ALL SELECT %s" % ", ".join(["%s"] * len(fields))] * (num_values - 1))
         return " ".join(res)
 
+
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'sqlite'
     # SQLite requires LIKE statements to include an ESCAPE clause if the value
@@ -433,6 +441,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
 FORMAT_QMARK_REGEX = re.compile(r'(?<!%)%s')
 
+
 class SQLiteCursorWrapper(Database.Cursor):
     """
     Django uses "format" style placeholders, but pysqlite2 uses "qmark" style.
@@ -452,6 +461,7 @@ class SQLiteCursorWrapper(Database.Cursor):
     def convert_query(self, query):
         return FORMAT_QMARK_REGEX.sub('?', query).replace('%%', '%')
 
+
 def _sqlite_date_extract(lookup_type, dt):
     if dt is None:
         return None
@@ -464,6 +474,7 @@ def _sqlite_date_extract(lookup_type, dt):
     else:
         return getattr(dt, lookup_type)
 
+
 def _sqlite_date_trunc(lookup_type, dt):
     try:
         dt = util.typecast_timestamp(dt)
@@ -476,6 +487,7 @@ def _sqlite_date_trunc(lookup_type, dt):
     elif lookup_type == 'day':
         return "%i-%02i-%02i" % (dt.year, dt.month, dt.day)
 
+
 def _sqlite_datetime_extract(lookup_type, dt, tzname):
     if dt is None:
         return None
@@ -490,6 +502,7 @@ def _sqlite_datetime_extract(lookup_type, dt, tzname):
     else:
         return getattr(dt, lookup_type)
 
+
 def _sqlite_datetime_trunc(lookup_type, dt, tzname):
     try:
         dt = util.typecast_timestamp(dt)
@@ -510,6 +523,7 @@ def _sqlite_datetime_trunc(lookup_type, dt, tzname):
     elif lookup_type == 'second':
         return "%i-%02i-%02i %02i:%02i:%02i" % (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second)
 
+
 def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
     try:
         dt = util.typecast_timestamp(dt)
@@ -524,5 +538,6 @@ def _sqlite_format_dtdelta(dt, conn, days, secs, usecs):
     # It will be formatted as "%Y-%m-%d" or "%Y-%m-%d %H:%M:%S[.%f]"
     return str(dt)
 
+
 def _sqlite_regexp(re_pattern, re_string):
     return bool(re.search(re_pattern, force_text(re_string))) if re_string is not None else False
diff --git a/django/db/backends/sqlite3/client.py b/django/db/backends/sqlite3/client.py
index 5b5b7326f2..6a3ad9e76f 100644
--- a/django/db/backends/sqlite3/client.py
+++ b/django/db/backends/sqlite3/client.py
@@ -3,6 +3,7 @@ import sys
 
 from django.db.backends import BaseDatabaseClient
 
+
 class DatabaseClient(BaseDatabaseClient):
     executable_name = 'sqlite3'
 
@@ -13,4 +14,3 @@ class DatabaseClient(BaseDatabaseClient):
             sys.exit(os.system(" ".join(args)))
         else:
             os.execvp(self.executable_name, args)
-
diff --git a/django/db/backends/sqlite3/creation.py b/django/db/backends/sqlite3/creation.py
index a9fb273f7a..435cee3436 100644
--- a/django/db/backends/sqlite3/creation.py
+++ b/django/db/backends/sqlite3/creation.py
@@ -1,36 +1,38 @@
 import os
 import sys
+
 from django.db.backends.creation import BaseDatabaseCreation
 from django.utils.six.moves import input
 
+
 class DatabaseCreation(BaseDatabaseCreation):
     # SQLite doesn't actually support most of these types, but it "does the right
     # thing" given more verbose field definitions, so leave them as is so that
     # schema inspection is more useful.
     data_types = {
-        'AutoField':                    'integer',
-        'BinaryField':                  'BLOB',
-        'BooleanField':                 'bool',
-        'CharField':                    'varchar(%(max_length)s)',
-        'CommaSeparatedIntegerField':   'varchar(%(max_length)s)',
-        'DateField':                    'date',
-        'DateTimeField':                'datetime',
-        'DecimalField':                 'decimal',
-        'FileField':                    'varchar(%(max_length)s)',
-        'FilePathField':                'varchar(%(max_length)s)',
-        'FloatField':                   'real',
-        'IntegerField':                 'integer',
-        'BigIntegerField':              'bigint',
-        'IPAddressField':               'char(15)',
-        'GenericIPAddressField':        'char(39)',
-        'NullBooleanField':             'bool',
-        'OneToOneField':                'integer',
-        'PositiveIntegerField':         'integer unsigned',
-        'PositiveSmallIntegerField':    'smallint unsigned',
-        'SlugField':                    'varchar(%(max_length)s)',
-        'SmallIntegerField':            'smallint',
-        'TextField':                    'text',
-        'TimeField':                    'time',
+        'AutoField': 'integer',
+        'BinaryField': 'BLOB',
+        'BooleanField': 'bool',
+        'CharField': 'varchar(%(max_length)s)',
+        'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
+        'DateField': 'date',
+        'DateTimeField': 'datetime',
+        'DecimalField': 'decimal',
+        'FileField': 'varchar(%(max_length)s)',
+        'FilePathField': 'varchar(%(max_length)s)',
+        'FloatField': 'real',
+        'IntegerField': 'integer',
+        'BigIntegerField': 'bigint',
+        'IPAddressField': 'char(15)',
+        'GenericIPAddressField': 'char(39)',
+        'NullBooleanField': 'bool',
+        'OneToOneField': 'integer',
+        'PositiveIntegerField': 'integer unsigned',
+        'PositiveSmallIntegerField': 'smallint unsigned',
+        'SlugField': 'varchar(%(max_length)s)',
+        'SmallIntegerField': 'smallint',
+        'TextField': 'text',
+        'TimeField': 'time',
     }
 
     def sql_for_pending_references(self, model, style, pending_references):
@@ -80,7 +82,6 @@ class DatabaseCreation(BaseDatabaseCreation):
         SQLite since the databases will be distinct despite having the same
         TEST_NAME. See http://www.sqlite.org/inmemorydb.html
         """
-        settings_dict = self.connection.settings_dict
         test_dbname = self._get_test_db_name()
         sig = [self.connection.settings_dict['NAME']]
         if test_dbname == ':memory:':
diff --git a/django/db/backends/sqlite3/introspection.py b/django/db/backends/sqlite3/introspection.py
index 799d6ec8fd..2e674bc05b 100644
--- a/django/db/backends/sqlite3/introspection.py
+++ b/django/db/backends/sqlite3/introspection.py
@@ -1,8 +1,11 @@
 import re
+
 from django.db.backends import BaseDatabaseIntrospection, FieldInfo
 
+
 field_size_re = re.compile(r'^\s*(?:var)?char\s*\(\s*(\d+)\s*\)\s*$')
 
+
 def get_field_size(name):
     """ Extract the size number from a "varchar(11)" type name """
     m = field_size_re.search(name)
@@ -46,6 +49,7 @@ class FlexibleFieldLookupDict(object):
                 return ('CharField', {'max_length': size})
             raise KeyError
 
+
 class DatabaseIntrospection(BaseDatabaseIntrospection):
     data_types_reverse = FlexibleFieldLookupDict()
 
@@ -76,7 +80,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         # Schema for this table
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
 
         # Walk through and look for references to other tables. SQLite doesn't
         # really have enforced references, but since it echoes out the SQL used
@@ -96,8 +100,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             result = cursor.fetchall()[0]
             other_table_results = result[0].strip()
             li, ri = other_table_results.index('('), other_table_results.rindex(')')
-            other_table_results = other_table_results[li+1:ri]
-
+            other_table_results = other_table_results[li + 1:ri]
 
             for other_index, other_desc in enumerate(other_table_results.split(',')):
                 other_desc = other_desc.strip()
@@ -121,7 +124,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         # Schema for this table
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
 
         # Walk through and look for references to other tables. SQLite doesn't
         # really have enforced references, but since it echoes out the SQL used
@@ -166,7 +169,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         # Don't use PRAGMA because that causes issues with some transactions
         cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
         results = cursor.fetchone()[0].strip()
-        results = results[results.index('(')+1:results.rindex(')')]
+        results = results[results.index('(') + 1:results.rindex(')')]
         for field_desc in results.split(','):
             field_desc = field_desc.strip()
             m = re.search('"(.*)".*PRIMARY KEY$', field_desc)
diff --git a/django/db/backends/util.py b/django/db/backends/util.py
index aa2601277a..f8157c50e7 100644
--- a/django/db/backends/util.py
+++ b/django/db/backends/util.py
@@ -85,20 +85,25 @@ class CursorDebugWrapper(CursorWrapper):
 def typecast_date(s):
     return datetime.date(*map(int, s.split('-'))) if s else None # returns None if s is null
 
+
 def typecast_time(s): # does NOT store time zone information
-    if not s: return None
+    if not s:
+        return None
     hour, minutes, seconds = s.split(':')
     if '.' in seconds: # check whether seconds have a fractional part
         seconds, microseconds = seconds.split('.')
     else:
         microseconds = '0'
-    return datetime.time(int(hour), int(minutes), int(seconds), int(float('.'+microseconds) * 1000000))
+    return datetime.time(int(hour), int(minutes), int(seconds), int(float('.' + microseconds) * 1000000))
+
 
 def typecast_timestamp(s): # does NOT store time zone information
     # "2005-07-29 15:48:00.590358-05"
     # "2005-07-29 09:56:00-05"
-    if not s: return None
-    if not ' ' in s: return typecast_date(s)
+    if not s:
+        return None
+    if not ' ' in s:
+        return typecast_date(s)
     d, t = s.split()
     # Extract timezone information, if it exists. Currently we just throw
     # it away, but in the future we may make use of it.
@@ -122,11 +127,13 @@ def typecast_timestamp(s): # does NOT store time zone information
         int(times[0]), int(times[1]), int(seconds),
         int((microseconds + '000000')[:6]), tzinfo)
 
+
 def typecast_decimal(s):
     if s is None or s == '':
         return None
     return decimal.Decimal(s)
 
+
 ###############################################
 # Converters from Python to database (string) #
 ###############################################
@@ -136,6 +143,7 @@ def rev_typecast_decimal(d):
         return None
     return str(d)
 
+
 def truncate_name(name, length=None, hash_len=4):
     """Shortens a string to a repeatable mangled version with the given length.
     """
@@ -143,7 +151,8 @@ def truncate_name(name, length=None, hash_len=4):
         return name
 
     hsh = hashlib.md5(force_bytes(name)).hexdigest()[:hash_len]
-    return '%s%s' % (name[:length-hash_len], hsh)
+    return '%s%s' % (name[:length - hash_len], hsh)
+
 
 def format_number(value, max_digits, decimal_places):
     """
diff --git a/django/db/models/__init__.py b/django/db/models/__init__.py
index b5dd1a58bc..4d310e480b 100644
--- a/django/db/models/__init__.py
+++ b/django/db/models/__init__.py
@@ -26,6 +26,7 @@ def permalink(func):
         (viewname, viewargs, viewkwargs)
     """
     from django.core.urlresolvers import reverse
+
     @wraps(func)
     def inner(*args, **kwargs):
         bits = func(*args, **kwargs)
diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index b89db1c563..1db3890204 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -3,6 +3,7 @@ Classes to represent the definitions of aggregate functions.
 """
 from django.db.models.constants import LOOKUP_SEP
 
+
 def refs_aggregate(lookup_parts, aggregates):
     """
     A little helper method to check if the lookup_parts contains references
@@ -15,6 +16,7 @@ def refs_aggregate(lookup_parts, aggregates):
             return True
     return False
 
+
 class Aggregate(object):
     """
     Default Aggregate definition.
@@ -58,23 +60,30 @@ class Aggregate(object):
         aggregate = klass(col, source=source, is_summary=is_summary, **self.extra)
         query.aggregates[alias] = aggregate
 
+
 class Avg(Aggregate):
     name = 'Avg'
 
+
 class Count(Aggregate):
     name = 'Count'
 
+
 class Max(Aggregate):
     name = 'Max'
 
+
 class Min(Aggregate):
     name = 'Min'
 
+
 class StdDev(Aggregate):
     name = 'StdDev'
 
+
 class Sum(Aggregate):
     name = 'Sum'
 
+
 class Variance(Aggregate):
     name = 'Variance'
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 17a4a14b8d..a2937f12c6 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -19,6 +19,7 @@ from django.db.models.query_utils import DeferredAttribute, deferred_class_facto
 from django.db.models.deletion import Collector
 from django.db.models.options import Options
 from django.db.models import signals
+from django.db.models.loading import register_models, get_model, MODELS_MODULE_NAME
 from django.utils.translation import ugettext_lazy as _
 from django.utils.functional import curry
 from django.utils.encoding import force_str, force_text
@@ -85,10 +86,22 @@ class ModelBase(type):
         base_meta = getattr(new_class, '_meta', None)
 
         if getattr(meta, 'app_label', None) is None:
-            # Figure out the app_label by looking one level up.
+            # Figure out the app_label by looking one level up from the package
+            # or module named 'models'. If no such package or module exists,
+            # fall back to looking one level up from the module this model is
+            # defined in.
+
             # For 'django.contrib.sites.models', this would be 'sites'.
+            # For 'geo.models.places' this would be 'geo'.
+
             model_module = sys.modules[new_class.__module__]
-            kwargs = {"app_label": model_module.__name__.split('.')[-2]}
+            package_components = model_module.__name__.split('.')
+            package_components.reverse()  # find the last occurrence of 'models'
+            try:
+                app_label_index = package_components.index(MODELS_MODULE_NAME) + 1
+            except ValueError:
+                app_label_index = 1
+            kwargs = {"app_label": package_components[app_label_index]}
         else:
             kwargs = {}
 
@@ -225,9 +238,9 @@ class ModelBase(type):
             # class
             for field in base._meta.virtual_fields:
                 if base._meta.abstract and field.name in field_names:
-                    raise FieldError('Local field %r in class %r clashes '\
-                                     'with field of similar name from '\
-                                     'abstract base class %r' % \
+                    raise FieldError('Local field %r in class %r clashes '
+                                     'with field of similar name from '
+                                     'abstract base class %r' %
                                         (field.name, name, base.__name__))
                 new_class.add_to_class(field.name, copy.deepcopy(field))
 
@@ -1007,8 +1020,6 @@ def get_absolute_url(opts, func, self, *args, **kwargs):
 # MISC #
 ########
 
-class Empty(object):
-    pass
 
 def simple_class_factory(model, attrs):
     """
@@ -1016,6 +1027,7 @@ def simple_class_factory(model, attrs):
     """
     return model
 
+
 def model_unpickle(model_id, attrs, factory):
     """
     Used to unpickle Model subclasses with deferred fields.
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index 6e0f3c434e..b4eea5fe71 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -4,6 +4,7 @@ from django.db.models.aggregates import refs_aggregate
 from django.db.models.constants import LOOKUP_SEP
 from django.utils import tree
 
+
 class ExpressionNode(tree.Node):
     """
     Base class for all query expressions.
@@ -128,6 +129,7 @@ class ExpressionNode(tree.Node):
             "Use .bitand() and .bitor() for bitwise logical operations."
         )
 
+
 class F(ExpressionNode):
     """
     An expression representing the value of the given field.
@@ -147,6 +149,7 @@ class F(ExpressionNode):
     def evaluate(self, evaluator, qn, connection):
         return evaluator.evaluate_leaf(self, qn, connection)
 
+
 class DateModifierNode(ExpressionNode):
     """
     Node that implements the following syntax:
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 9263f81184..0410815c92 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+import collections
 import copy
 import datetime
 import decimal
@@ -17,7 +18,6 @@ from django.core import exceptions, validators
 from django.utils.datastructures import DictWrapper
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.functional import curry, total_ordering
-from django.utils.itercompat import is_iterator
 from django.utils.text import capfirst
 from django.utils import timezone
 from django.utils.translation import ugettext_lazy as _
@@ -25,9 +25,11 @@ from django.utils.encoding import smart_text, force_text, force_bytes
 from django.utils.ipv6 import clean_ipv6_address
 from django.utils import six
 
+
 class Empty(object):
     pass
 
+
 class NOT_PROVIDED:
     pass
 
@@ -35,12 +37,15 @@ class NOT_PROVIDED:
 # of most "choices" lists.
 BLANK_CHOICE_DASH = [("", "---------")]
 
+
 def _load_field(app_label, model_name, field_name):
     return get_model(app_label, model_name)._meta.get_field_by_name(field_name)[0]
 
+
 class FieldDoesNotExist(Exception):
     pass
 
+
 # A guide to Field parameters:
 #
 #   * name:      The name of the field specifed in the model.
@@ -61,6 +66,7 @@ def _empty(of_cls):
     new.__class__ = of_cls
     return new
 
+
 @total_ordering
 class Field(object):
     """Base class for all field types"""
@@ -464,12 +470,12 @@ class Field(object):
         if hasattr(value, '_prepare'):
             return value._prepare()
 
-        if lookup_type in (
-                'iexact', 'contains', 'icontains',
-                'startswith', 'istartswith', 'endswith', 'iendswith',
-                'month', 'day', 'week_day', 'hour', 'minute', 'second',
-                'isnull', 'search', 'regex', 'iregex',
-            ):
+        if lookup_type in {
+            'iexact', 'contains', 'icontains',
+            'startswith', 'istartswith', 'endswith', 'iendswith',
+            'month', 'day', 'week_day', 'hour', 'minute', 'second',
+            'isnull', 'search', 'regex', 'iregex',
+        }:
             return value
         elif lookup_type in ('exact', 'gt', 'gte', 'lt', 'lte'):
             return self.get_prep_value(value)
@@ -599,7 +605,7 @@ class Field(object):
         return bound_field_class(self, fieldmapping, original)
 
     def _get_choices(self):
-        if is_iterator(self._choices):
+        if isinstance(self._choices, collections.Iterator):
             choices, self._choices = tee(self._choices)
             return choices
         else:
@@ -613,7 +619,7 @@ class Field(object):
             if isinstance(value, (list, tuple)):
                 flat.extend(value)
             else:
-                flat.append((choice,value))
+                flat.append((choice, value))
         return flat
     flatchoices = property(_get_flatchoices)
 
@@ -732,6 +738,7 @@ class AutoField(Field):
     def formfield(self, **kwargs):
         return None
 
+
 class BooleanField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -786,13 +793,13 @@ class BooleanField(Field):
         if self.choices:
             include_blank = (self.null or
                              not (self.has_default() or 'initial' in kwargs))
-            defaults = {'choices': self.get_choices(
-                                       include_blank=include_blank)}
+            defaults = {'choices': self.get_choices(include_blank=include_blank)}
         else:
             defaults = {'form_class': forms.BooleanField}
         defaults.update(kwargs)
         return super(BooleanField, self).formfield(**defaults)
 
+
 class CharField(Field):
     description = _("String (up to %(max_length)s)")
 
@@ -819,6 +826,7 @@ class CharField(Field):
         defaults.update(kwargs)
         return super(CharField, self).formfield(**defaults)
 
+
 # TODO: Maybe move this into contrib, because it's specialized.
 class CommaSeparatedIntegerField(CharField):
     default_validators = [validators.validate_comma_separated_integer_list]
@@ -833,6 +841,7 @@ class CommaSeparatedIntegerField(CharField):
         defaults.update(kwargs)
         return super(CommaSeparatedIntegerField, self).formfield(**defaults)
 
+
 class DateField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -905,7 +914,7 @@ class DateField(Field):
             return super(DateField, self).pre_save(model_instance, add)
 
     def contribute_to_class(self, cls, name):
-        super(DateField,self).contribute_to_class(cls, name)
+        super(DateField, self).contribute_to_class(cls, name)
         if not self.null:
             setattr(cls, 'get_next_by_%s' % self.name,
                 curry(cls._get_next_or_previous_by_FIELD, field=self,
@@ -939,6 +948,7 @@ class DateField(Field):
         defaults.update(kwargs)
         return super(DateField, self).formfield(**defaults)
 
+
 class DateTimeField(DateField):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1045,6 +1055,7 @@ class DateTimeField(DateField):
         defaults.update(kwargs)
         return super(DateTimeField, self).formfield(**defaults)
 
+
 class DecimalField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1116,6 +1127,7 @@ class DecimalField(Field):
         defaults.update(kwargs)
         return super(DecimalField, self).formfield(**defaults)
 
+
 class EmailField(CharField):
     default_validators = [validators.validate_email]
     description = _("Email address")
@@ -1142,13 +1154,14 @@ class EmailField(CharField):
         defaults.update(kwargs)
         return super(EmailField, self).formfield(**defaults)
 
+
 class FilePathField(Field):
     description = _("File path")
 
     def __init__(self, verbose_name=None, name=None, path='', match=None,
                  recursive=False, allow_files=True, allow_folders=False, **kwargs):
         self.path, self.match, self.recursive = path, match, recursive
-        self.allow_files, self.allow_folders =  allow_files, allow_folders
+        self.allow_files, self.allow_folders = allow_files, allow_folders
         kwargs['max_length'] = kwargs.get('max_length', 100)
         Field.__init__(self, verbose_name, name, **kwargs)
 
@@ -1183,6 +1196,7 @@ class FilePathField(Field):
     def get_internal_type(self):
         return "FilePathField"
 
+
 class FloatField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1215,6 +1229,7 @@ class FloatField(Field):
         defaults.update(kwargs)
         return super(FloatField, self).formfield(**defaults)
 
+
 class IntegerField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1253,6 +1268,7 @@ class IntegerField(Field):
         defaults.update(kwargs)
         return super(IntegerField, self).formfield(**defaults)
 
+
 class BigIntegerField(IntegerField):
     empty_strings_allowed = False
     description = _("Big (8 byte) integer")
@@ -1267,6 +1283,7 @@ class BigIntegerField(IntegerField):
         defaults.update(kwargs)
         return super(BigIntegerField, self).formfield(**defaults)
 
+
 class IPAddressField(Field):
     empty_strings_allowed = False
     description = _("IPv4 address")
@@ -1288,6 +1305,7 @@ class IPAddressField(Field):
         defaults.update(kwargs)
         return super(IPAddressField, self).formfield(**defaults)
 
+
 class GenericIPAddressField(Field):
     empty_strings_allowed = True
     description = _("IP address")
@@ -1336,7 +1354,10 @@ class GenericIPAddressField(Field):
         return value
 
     def formfield(self, **kwargs):
-        defaults = {'form_class': forms.GenericIPAddressField}
+        defaults = {
+            'protocol': self.protocol,
+            'form_class': forms.GenericIPAddressField,
+        }
         defaults.update(kwargs)
         return super(GenericIPAddressField, self).formfield(**defaults)
 
@@ -1403,6 +1424,7 @@ class NullBooleanField(Field):
         defaults.update(kwargs)
         return super(NullBooleanField, self).formfield(**defaults)
 
+
 class PositiveIntegerField(IntegerField):
     description = _("Positive integer")
 
@@ -1414,6 +1436,7 @@ class PositiveIntegerField(IntegerField):
         defaults.update(kwargs)
         return super(PositiveIntegerField, self).formfield(**defaults)
 
+
 class PositiveSmallIntegerField(IntegerField):
     description = _("Positive small integer")
 
@@ -1425,6 +1448,7 @@ class PositiveSmallIntegerField(IntegerField):
         defaults.update(kwargs)
         return super(PositiveSmallIntegerField, self).formfield(**defaults)
 
+
 class SlugField(CharField):
     default_validators = [validators.validate_slug]
     description = _("Slug (up to %(max_length)s)")
@@ -1454,12 +1478,14 @@ class SlugField(CharField):
         defaults.update(kwargs)
         return super(SlugField, self).formfield(**defaults)
 
+
 class SmallIntegerField(IntegerField):
     description = _("Small integer")
 
     def get_internal_type(self):
         return "SmallIntegerField"
 
+
 class TextField(Field):
     description = _("Text")
 
@@ -1476,6 +1502,7 @@ class TextField(Field):
         defaults.update(kwargs)
         return super(TextField, self).formfield(**defaults)
 
+
 class TimeField(Field):
     empty_strings_allowed = False
     default_error_messages = {
@@ -1559,6 +1586,7 @@ class TimeField(Field):
         defaults.update(kwargs)
         return super(TimeField, self).formfield(**defaults)
 
+
 class URLField(CharField):
     default_validators = [validators.URLValidator()]
     description = _("URL")
@@ -1582,6 +1610,7 @@ class URLField(CharField):
         defaults.update(kwargs)
         return super(URLField, self).formfield(**defaults)
 
+
 class BinaryField(Field):
     description = _("Raw binary data")
     empty_values = [None, b'']
diff --git a/django/db/models/fields/files.py b/django/db/models/fields/files.py
index 7663c8ab90..311f74a905 100644
--- a/django/db/models/fields/files.py
+++ b/django/db/models/fields/files.py
@@ -11,6 +11,7 @@ from django.utils.encoding import force_str, force_text
 from django.utils import six
 from django.utils.translation import ugettext_lazy as _
 
+
 class FieldFile(File):
     def __init__(self, instance, field, name):
         super(FieldFile, self).__init__(None, name)
@@ -135,6 +136,7 @@ class FieldFile(File):
         # be restored later, by FileDescriptor below.
         return {'name': self.name, 'closed': False, '_committed': True, '_file': None}
 
+
 class FileDescriptor(object):
     """
     The descriptor for the file attribute on the model instance. Returns a
@@ -205,6 +207,7 @@ class FileDescriptor(object):
     def __set__(self, instance, value):
         instance.__dict__[self.field.name] = value
 
+
 class FileField(Field):
 
     # The class to wrap instance attributes in. Accessing the file object off
@@ -300,6 +303,7 @@ class FileField(Field):
         defaults.update(kwargs)
         return super(FileField, self).formfield(**defaults)
 
+
 class ImageFileDescriptor(FileDescriptor):
     """
     Just like the FileDescriptor, but for ImageFields. The only difference is
@@ -321,14 +325,15 @@ class ImageFileDescriptor(FileDescriptor):
         if previous_file is not None:
             self.field.update_dimension_fields(instance, force=True)
 
-class ImageFieldFile(ImageFile, FieldFile):
 
+class ImageFieldFile(ImageFile, FieldFile):
     def delete(self, save=True):
         # Clear the image dimensions cache
         if hasattr(self, '_dimensions_cache'):
             del self._dimensions_cache
         super(ImageFieldFile, self).delete(save)
 
+
 class ImageField(FileField):
     attr_class = ImageFieldFile
     descriptor_class = ImageFileDescriptor
diff --git a/django/db/models/fields/proxy.py b/django/db/models/fields/proxy.py
index c0cc873f4c..29c782b59a 100644
--- a/django/db/models/fields/proxy.py
+++ b/django/db/models/fields/proxy.py
@@ -5,6 +5,7 @@ have the same attributes as fields sometimes (avoids a lot of special casing).
 
 from django.db.models import fields
 
+
 class OrderWrt(fields.IntegerField):
     """
     A proxy for the _order database field that is used when
diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 480c77ab77..5a7718e880 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -211,7 +211,7 @@ class SingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjectDescri
 
         # If null=True, we can assign null here, but otherwise the value needs
         # to be an instance of the related class.
-        if value is None and self.related.field.null == False:
+        if value is None and self.related.field.null is False:
             raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                 (instance._meta.object_name, self.related.get_accessor_name()))
         elif value is not None and not isinstance(value, self.related.model):
@@ -310,7 +310,7 @@ class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjec
     def __set__(self, instance, value):
         # If null=True, we can assign null here, but otherwise the value needs
         # to be an instance of the related class.
-        if value is None and self.field.null == False:
+        if value is None and self.field.null is False:
             raise ValueError('Cannot assign None: "%s.%s" does not allow null values.' %
                                 (instance._meta.object_name, self.field.name))
         elif value is not None and not isinstance(value, self.field.rel.to):
@@ -395,7 +395,7 @@ class ForeignRelatedObjectsDescriptor(object):
             def __init__(self, instance):
                 super(RelatedManager, self).__init__()
                 self.instance = instance
-                self.core_filters= {'%s__exact' % rel_field.name: instance}
+                self.core_filters = {'%s__exact' % rel_field.name: instance}
                 self.model = rel_model
 
             def get_queryset(self):
@@ -510,7 +510,6 @@ def create_many_related_manager(superclass, rel):
                                  "a many-to-many relationship can be used." %
                                  instance.__class__.__name__)
 
-
         def _get_fk_val(self, obj, field_name):
             """
             Returns the correct value for this relationship's foreign key. This
@@ -821,6 +820,7 @@ class ReverseManyRelatedObjectsDescriptor(object):
         manager.clear()
         manager.add(*value)
 
+
 class ForeignObjectRel(object):
     def __init__(self, field, to, related_name=None, limit_choices_to=None,
                  parent_link=False, on_delete=None, related_query_name=None):
@@ -858,6 +858,7 @@ class ForeignObjectRel(object):
         # example custom multicolumn joins currently have no remote field).
         self.field_name = None
 
+
 class ManyToOneRel(ForeignObjectRel):
     def __init__(self, field, to, field_name, related_name=None, limit_choices_to=None,
                  parent_link=False, on_delete=None, related_query_name=None):
@@ -1125,7 +1126,7 @@ class ForeignKey(ForeignObject):
     def __init__(self, to, to_field=None, rel_class=ManyToOneRel,
                  db_constraint=True, **kwargs):
         try:
-            to_name = to._meta.object_name.lower()
+            to._meta.object_name.lower()
         except AttributeError:  # to._meta doesn't exist, so it must be RECURSIVE_RELATIONSHIP_CONSTANT
             assert isinstance(to, six.string_types), "%s(%r) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string %r" % (self.__class__.__name__, to, RECURSIVE_RELATIONSHIP_CONSTANT)
         else:
@@ -1162,7 +1163,6 @@ class ForeignKey(ForeignObject):
         if self.rel.on_delete is not CASCADE:
             kwargs['on_delete'] = self.rel.on_delete
         # Rel needs more work.
-        rel = self.rel
         if self.rel.field_name:
             kwargs['to_field'] = self.rel.field_name
         if isinstance(self.rel.to, six.string_types):
@@ -1193,8 +1193,8 @@ class ForeignKey(ForeignObject):
 
         using = router.db_for_read(model_instance.__class__, instance=model_instance)
         qs = self.rel.to._default_manager.using(using).filter(
-                **{self.rel.field_name: value}
-             )
+          **{self.rel.field_name: value}
+         )
         qs = qs.complex_filter(self.rel.limit_choices_to)
         if not qs.exists():
             raise exceptions.ValidationError(
@@ -1222,7 +1222,7 @@ class ForeignKey(ForeignObject):
         return field_default
 
     def get_db_prep_save(self, value, connection):
-        if value == '' or value == None:
+        if value == '' or value is None:
             return None
         else:
             return self.related_field.get_db_prep_save(value,
@@ -1393,7 +1393,6 @@ class ManyToManyField(RelatedField):
         if "help_text" in kwargs:
             del kwargs['help_text']
         # Rel needs more work.
-        rel = self.rel
         if isinstance(self.rel.to, six.string_types):
             kwargs['to'] = self.rel.to
         else:
diff --git a/django/db/models/fields/subclassing.py b/django/db/models/fields/subclassing.py
index e6153aefe0..591adb7121 100644
--- a/django/db/models/fields/subclassing.py
+++ b/django/db/models/fields/subclassing.py
@@ -7,6 +7,7 @@ to_python() and the other necessary methods and everything will work
 seamlessly.
 """
 
+
 class SubfieldBase(type):
     """
     A metaclass for custom Field subclasses. This ensures the model's attribute
@@ -19,6 +20,7 @@ class SubfieldBase(type):
         )
         return new_class
 
+
 class Creator(object):
     """
     A placeholder class that provides a way to set the attribute on the model.
@@ -34,6 +36,7 @@ class Creator(object):
     def __set__(self, obj, value):
         obj.__dict__[self.field.name] = self.field.to_python(value)
 
+
 def make_contrib(superclass, func=None):
     """
     Returns a suitable contribute_to_class() method for the Field subclass.
diff --git a/django/db/models/loading.py b/django/db/models/loading.py
index c1e394327f..df3be5fe9b 100644
--- a/django/db/models/loading.py
+++ b/django/db/models/loading.py
@@ -15,9 +15,13 @@ import os
 __all__ = ('get_apps', 'get_app', 'get_models', 'get_model', 'register_models',
         'load_app', 'app_cache_ready')
 
+MODELS_MODULE_NAME = 'models'
+
+
 class UnavailableApp(Exception):
     pass
 
+
 def _initialize():
     """
     Returns a dictionary to be used as the initial value of the
@@ -118,12 +122,12 @@ class BaseAppCache(object):
         self.nesting_level += 1
         app_module = import_module(app_name)
         try:
-            models = import_module('.models', app_name)
+            models = import_module('.' + MODELS_MODULE_NAME, app_name)
         except ImportError:
             self.nesting_level -= 1
             # If the app doesn't have a models module, we can just ignore the
             # ImportError and return no models for it.
-            if not module_has_submodule(app_module, 'models'):
+            if not module_has_submodule(app_module, MODELS_MODULE_NAME):
                 return None
             # But if the app does have a models module, we need to figure out
             # whether to suppress or propagate the error. If can_postpone is
diff --git a/django/db/models/manager.py b/django/db/models/manager.py
index 6817c9c8ee..b369aedb64 100644
--- a/django/db/models/manager.py
+++ b/django/db/models/manager.py
@@ -6,6 +6,7 @@ from django.db.models.fields import FieldDoesNotExist
 from django.utils import six
 from django.utils.deprecation import RenameMethodsBase
 
+
 def ensure_default_manager(sender, **kwargs):
     """
     Ensures that a Model subclass contains a default manager  and sets the
@@ -153,6 +154,9 @@ class Manager(six.with_metaclass(RenameManagerMethods)):
     def get_or_create(self, **kwargs):
         return self.get_queryset().get_or_create(**kwargs)
 
+    def update_or_create(self, **kwargs):
+        return self.get_queryset().update_or_create(**kwargs)
+
     def create(self, **kwargs):
         return self.get_queryset().create(**kwargs)
 
@@ -245,7 +249,7 @@ class ManagerDescriptor(object):
         self.manager = manager
 
     def __get__(self, instance, type=None):
-        if instance != None:
+        if instance is not None:
             raise AttributeError("Manager isn't accessible via %s instances" % type.__name__)
         return self.manager
 
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 34d8eaa6ff..811e917764 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -19,6 +19,10 @@ from django.utils.functional import partition
 from django.utils import six
 from django.utils import timezone
 
+# The maximum number (one less than the max to be precise) of results to fetch
+# in a get() query
+MAX_GET_RESULTS = 20
+
 # The maximum number of items to display in a QuerySet.__repr__
 REPR_OUTPUT_SIZE = 20
 
@@ -297,6 +301,7 @@ class QuerySet(object):
         clone = self.filter(*args, **kwargs)
         if self.query.can_filter():
             clone = clone.order_by()
+        clone = clone[:MAX_GET_RESULTS + 1]
         num = len(clone)
         if num == 1:
             return clone._result_cache[0]
@@ -305,8 +310,11 @@ class QuerySet(object):
                 "%s matching query does not exist." %
                 self.model._meta.object_name)
         raise self.model.MultipleObjectsReturned(
-            "get() returned more than one %s -- it returned %s!" %
-            (self.model._meta.object_name, num))
+            "get() returned more than one %s -- it returned %s!" % (
+                self.model._meta.object_name,
+                num if num <= MAX_GET_RESULTS else 'more than %s' % MAX_GET_RESULTS
+            )
+        )
 
     def create(self, **kwargs):
         """
@@ -351,42 +359,89 @@ class QuerySet(object):
                 if objs_with_pk:
                     self._batched_insert(objs_with_pk, fields, batch_size)
                 if objs_without_pk:
-                    fields= [f for f in fields if not isinstance(f, AutoField)]
+                    fields = [f for f in fields if not isinstance(f, AutoField)]
                     self._batched_insert(objs_without_pk, fields, batch_size)
 
         return objs
 
-    def get_or_create(self, **kwargs):
+    def get_or_create(self, defaults=None, **kwargs):
         """
         Looks up an object with the given kwargs, creating one if necessary.
         Returns a tuple of (object, created), where created is a boolean
         specifying whether an object was created.
         """
-        defaults = kwargs.pop('defaults', {})
-        lookup = kwargs.copy()
-        for f in self.model._meta.fields:
-            if f.attname in lookup:
-                lookup[f.name] = lookup.pop(f.attname)
+        lookup, params, _ = self._extract_model_params(defaults, **kwargs)
         try:
             self._for_write = True
             return self.get(**lookup), False
         except self.model.DoesNotExist:
+            return self._create_object_from_params(lookup, params)
+
+    def update_or_create(self, defaults=None, **kwargs):
+        """
+        Looks up an object with the given kwargs, updating one with defaults
+        if it exists, otherwise creates a new one.
+        Returns a tuple (object, created), where created is a boolean
+        specifying whether an object was created.
+        """
+        lookup, params, filtered_defaults = self._extract_model_params(defaults, **kwargs)
+        try:
+            self._for_write = True
+            obj = self.get(**lookup)
+        except self.model.DoesNotExist:
+            obj, created = self._create_object_from_params(lookup, params)
+            if created:
+                return obj, created
+        for k, v in six.iteritems(filtered_defaults):
+            setattr(obj, k, v)
+        try:
+            sid = transaction.savepoint(using=self.db)
+            obj.save(update_fields=filtered_defaults.keys(), using=self.db)
+            transaction.savepoint_commit(sid, using=self.db)
+            return obj, False
+        except DatabaseError:
+            transaction.savepoint_rollback(sid, using=self.db)
+            six.reraise(sys.exc_info())
+
+    def _create_object_from_params(self, lookup, params):
+        """
+        Tries to create an object using passed params.
+        Used by get_or_create and update_or_create
+        """
+        try:
+            obj = self.model(**params)
+            sid = transaction.savepoint(using=self.db)
+            obj.save(force_insert=True, using=self.db)
+            transaction.savepoint_commit(sid, using=self.db)
+            return obj, True
+        except DatabaseError:
+            transaction.savepoint_rollback(sid, using=self.db)
+            exc_info = sys.exc_info()
             try:
-                params = dict((k, v) for k, v in kwargs.items() if LOOKUP_SEP not in k)
-                params.update(defaults)
-                obj = self.model(**params)
-                sid = transaction.savepoint(using=self.db)
-                obj.save(force_insert=True, using=self.db)
-                transaction.savepoint_commit(sid, using=self.db)
-                return obj, True
-            except DatabaseError:
-                transaction.savepoint_rollback(sid, using=self.db)
-                exc_info = sys.exc_info()
-                try:
-                    return self.get(**lookup), False
-                except self.model.DoesNotExist:
-                    # Re-raise the DatabaseError with its original traceback.
-                    six.reraise(*exc_info)
+                return self.get(**lookup), False
+            except self.model.DoesNotExist:
+                # Re-raise the DatabaseError with its original traceback.
+                six.reraise(*exc_info)
+
+    def _extract_model_params(self, defaults, **kwargs):
+        """
+        Prepares `lookup` (kwargs that are valid model attributes), `params`
+        (for creating a model instance) and `filtered_defaults` (defaults
+        that are valid model attributes) based on given kwargs; for use by
+        get_or_create and update_or_create.
+        """
+        defaults = defaults or {}
+        filtered_defaults = {}
+        lookup = kwargs.copy()
+        for f in self.model._meta.fields:
+            # Filter out fields that don't belongs to the model.
+            if f.attname in lookup:
+                lookup[f.name] = lookup.pop(f.attname)
+            if f.attname in defaults:
+                filtered_defaults[f.name] = defaults.pop(f.attname)
+        params = dict((k, v) for k, v in kwargs.items() if LOOKUP_SEP not in k)
+        params.update(filtered_defaults)
+        return lookup, params, filtered_defaults
 
     def _earliest_or_latest(self, field_name=None, direction="-"):
         """
@@ -638,7 +693,7 @@ class QuerySet(object):
         obj.query.select_for_update_nowait = nowait
         return obj
 
-    def select_related(self, *fields, **kwargs):
+    def select_related(self, *fields):
         """
         Returns a new QuerySet instance that will select related objects.
 
@@ -647,9 +702,6 @@ class QuerySet(object):
 
         If select_related(None) is called, the list is cleared.
         """
-        if kwargs:
-            raise TypeError('Unexpected keyword arguments to select_related: %s'
-                    % (list(kwargs),))
         obj = self._clone()
         if fields == (None,):
             obj.query.select_related = False
@@ -821,7 +873,7 @@ class QuerySet(object):
             return
         ops = connections[self.db].ops
         batch_size = (batch_size or max(ops.bulk_batch_size(fields, objs), 1))
-        for batch in [objs[i:i+batch_size]
+        for batch in [objs[i:i + batch_size]
                       for i in range(0, len(objs), batch_size)]:
             self.model._base_manager._insert(batch, fields=fields,
                                              using=self.db)
@@ -902,10 +954,12 @@ class QuerySet(object):
     # empty" result.
     value_annotation = True
 
+
 class InstanceCheckMeta(type):
     def __instancecheck__(self, instance):
         return instance.query.is_empty()
 
+
 class EmptyQuerySet(six.with_metaclass(InstanceCheckMeta)):
     """
     Marker class usable for checking if a queryset is empty by .none():
@@ -915,6 +969,7 @@ class EmptyQuerySet(six.with_metaclass(InstanceCheckMeta)):
     def __init__(self, *args, **kwargs):
         raise TypeError("EmptyQuerySet can't be instantiated")
 
+
 class ValuesQuerySet(QuerySet):
     def __init__(self, *args, **kwargs):
         super(ValuesQuerySet, self).__init__(*args, **kwargs)
@@ -1243,7 +1298,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
                                                          only_load.get(o.model), reverse=True):
                 next = requested[o.field.related_query_name()]
                 parent = klass if issubclass(o.model, klass) else None
-                klass_info = get_klass_info(o.model, max_depth=max_depth, cur_depth=cur_depth+1,
+                klass_info = get_klass_info(o.model, max_depth=max_depth, cur_depth=cur_depth + 1,
                                             requested=next, only_load=only_load, from_parent=parent)
                 reverse_related_fields.append((o.field, klass_info))
     if field_names:
@@ -1254,7 +1309,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
     return klass, field_names, field_count, related_fields, reverse_related_fields, pk_idx
 
 
-def get_cached_row(row, index_start, using,  klass_info, offset=0,
+def get_cached_row(row, index_start, using, klass_info, offset=0,
                    parent_data=()):
     """
     Helper function that recursively returns an object with the specified
@@ -1279,11 +1334,10 @@ def get_cached_row(row, index_start, using,  klass_info, offset=0,
         return None
     klass, field_names, field_count, related_fields, reverse_related_fields, pk_idx = klass_info
 
-
-    fields = row[index_start : index_start + field_count]
+    fields = row[index_start:index_start + field_count]
     # If the pk column is None (or the Oracle equivalent ''), then the related
     # object must be non-existent - set the relation to None.
-    if fields[pk_idx] == None or fields[pk_idx] == '':
+    if fields[pk_idx] is None or fields[pk_idx] == '':
         obj = None
     elif field_names:
         fields = list(fields)
@@ -1513,8 +1567,6 @@ def prefetch_related_objects(result_cache, related_lookups):
     if len(result_cache) == 0:
         return # nothing to do
 
-    model = result_cache[0].__class__
-
     # We need to be able to dynamically add to the list of prefetch_related
     # lookups that we look up (see below).  So we need some book keeping to
     # ensure we don't do duplicate work.
@@ -1541,7 +1593,7 @@ def prefetch_related_objects(result_cache, related_lookups):
             if len(obj_list) == 0:
                 break
 
-            current_lookup = LOOKUP_SEP.join(attrs[0:level+1])
+            current_lookup = LOOKUP_SEP.join(attrs[:level + 1])
             if current_lookup in done_queries:
                 # Skip any prefetching, and any object preparation
                 obj_list = done_queries[current_lookup]
diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index ee7a56a26c..2a92978beb 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -30,6 +30,7 @@ class QueryWrapper(object):
     def as_sql(self, qn=None, connection=None):
         return self.data
 
+
 class Q(tree.Node):
     """
     Encapsulates filters as objects that can then be combined logically (using
@@ -74,6 +75,7 @@ class Q(tree.Node):
                 clone.children.append(child)
         return clone
 
+
 class DeferredAttribute(object):
     """
     A wrapper for a deferred-loading field. When the value is read from this
@@ -99,8 +101,7 @@ class DeferredAttribute(object):
             try:
                 f = opts.get_field_by_name(self.field_name)[0]
             except FieldDoesNotExist:
-                f = [f for f in opts.fields
-                     if f.attname == self.field_name][0]
+                f = [f for f in opts.fields if f.attname == self.field_name][0]
             name = f.name
             # Let's see if the field is part of the parent chain. If so we
             # might be able to reuse the already loaded value. Refs #18343.
@@ -174,6 +175,7 @@ def select_related_descend(field, restricted, requested, load_fields, reverse=Fa
             return False
     return True
 
+
 # This function is needed because data descriptors must be defined on a class
 # object, not an instance, to have any effect.
 
diff --git a/django/db/models/related.py b/django/db/models/related.py
index 4b00dd343b..ba2a90c545 100644
--- a/django/db/models/related.py
+++ b/django/db/models/related.py
@@ -10,6 +10,7 @@ PathInfo = namedtuple('PathInfo',
                       'from_opts to_opts target_fields join_field '
                       'm2m direct')
 
+
 class RelatedObject(object):
     def __init__(self, parent_model, model, field):
         self.parent_model = parent_model
diff --git a/django/db/models/sql/aggregates.py b/django/db/models/sql/aggregates.py
index 2bd2b2f76f..9fc5fe8a5b 100644
--- a/django/db/models/sql/aggregates.py
+++ b/django/db/models/sql/aggregates.py
@@ -9,6 +9,7 @@ from django.db.models.fields import IntegerField, FloatField
 ordinal_aggregate_field = IntegerField()
 computed_aggregate_field = FloatField()
 
+
 class Aggregate(object):
     """
     Default SQL Aggregate.
@@ -93,6 +94,7 @@ class Avg(Aggregate):
     is_computed = True
     sql_function = 'AVG'
 
+
 class Count(Aggregate):
     is_ordinal = True
     sql_function = 'COUNT'
@@ -101,12 +103,15 @@ class Count(Aggregate):
     def __init__(self, col, distinct=False, **extra):
         super(Count, self).__init__(col, distinct='DISTINCT ' if distinct else '', **extra)
 
+
 class Max(Aggregate):
     sql_function = 'MAX'
 
+
 class Min(Aggregate):
     sql_function = 'MIN'
 
+
 class StdDev(Aggregate):
     is_computed = True
 
@@ -114,9 +119,11 @@ class StdDev(Aggregate):
         super(StdDev, self).__init__(col, **extra)
         self.sql_function = 'STDDEV_SAMP' if sample else 'STDDEV_POP'
 
+
 class Sum(Aggregate):
     sql_function = 'SUM'
 
+
 class Variance(Aggregate):
     is_computed = True
 
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index f70750abed..e17cb3f616 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -688,7 +688,7 @@ class SQLCompiler(object):
                 # the relation, which is always nullable.
                 new_nullable = True
                 table = model._meta.db_table
-                self.fill_related_selections(model._meta, table, cur_depth+1,
+                self.fill_related_selections(model._meta, table, cur_depth + 1,
                     next, restricted, new_nullable)
 
     def deferred_to_columns(self):
@@ -750,6 +750,16 @@ class SQLCompiler(object):
 
                 yield row
 
+    def has_results(self):
+        """
+        Backends (e.g. NoSQL) can override this in order to use optimized
+        versions of "query has any results."
+        """
+        # This is always executed on a query clone, so we can modify self.query
+        self.query.add_extra({'a': 1}, None, None, None, None, None)
+        self.query.set_extra_mask(['a'])
+        return bool(self.execute_sql(SINGLE))
+
     def execute_sql(self, result_type=MULTI):
         """
         Run the query against the database and returns the result(s). The
@@ -915,6 +925,7 @@ class SQLDeleteCompiler(SQLCompiler):
             result.append('WHERE %s' % where)
         return ' '.join(result), tuple(params)
 
+
 class SQLUpdateCompiler(SQLCompiler):
     def as_sql(self):
         """
@@ -1029,6 +1040,7 @@ class SQLUpdateCompiler(SQLCompiler):
         for alias in self.query.tables[1:]:
             self.query.alias_refcount[alias] = 0
 
+
 class SQLAggregateCompiler(SQLCompiler):
     def as_sql(self, qn=None):
         """
@@ -1050,6 +1062,7 @@ class SQLAggregateCompiler(SQLCompiler):
         params = params + self.query.sub_params
         return sql, params
 
+
 class SQLDateCompiler(SQLCompiler):
     def results_iter(self):
         """
@@ -1075,6 +1088,7 @@ class SQLDateCompiler(SQLCompiler):
                     date = date.date()
                 yield date
 
+
 class SQLDateTimeCompiler(SQLCompiler):
     def results_iter(self):
         """
@@ -1107,6 +1121,7 @@ class SQLDateTimeCompiler(SQLCompiler):
                     datetime = timezone.make_aware(datetime, self.query.tzinfo)
                 yield datetime
 
+
 def order_modified_iter(cursor, trim, sentinel):
     """
     Yields blocks of rows from a cursor. We use this iterator in the special
diff --git a/django/db/models/sql/datastructures.py b/django/db/models/sql/datastructures.py
index daaabbe6da..76b3db5b35 100644
--- a/django/db/models/sql/datastructures.py
+++ b/django/db/models/sql/datastructures.py
@@ -3,9 +3,11 @@ Useful auxilliary data structures for query construction. Not useful outside
 the SQL domain.
 """
 
+
 class EmptyResultSet(Exception):
     pass
 
+
 class MultiJoin(Exception):
     """
     Used by join construction code to indicate the point at which a
@@ -17,12 +19,10 @@ class MultiJoin(Exception):
         # The path travelled, this includes the path to the multijoin.
         self.names_with_path = path_with_names
 
+
 class Empty(object):
     pass
 
-class RawValue(object):
-    def __init__(self, value):
-        self.value = value
 
 class Date(object):
     """
@@ -42,6 +42,7 @@ class Date(object):
             col = self.col
         return connection.ops.date_trunc_sql(self.lookup_type, col), []
 
+
 class DateTime(object):
     """
     Add a datetime selection column.
diff --git a/django/db/models/sql/expressions.py b/django/db/models/sql/expressions.py
index 62adf79d87..f9a8929974 100644
--- a/django/db/models/sql/expressions.py
+++ b/django/db/models/sql/expressions.py
@@ -1,7 +1,9 @@
+import copy
+
 from django.core.exceptions import FieldError
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import FieldDoesNotExist
-import copy
+
 
 class SQLEvaluator(object):
     def __init__(self, expression, query, allow_joins=True, reuse=None):
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index 75e8e7540d..2a9b8ef826 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -401,12 +401,10 @@ class Query(object):
     def has_results(self, using):
         q = self.clone()
         q.clear_select_clause()
-        q.add_extra({'a': 1}, None, None, None, None, None)
-        q.set_extra_mask(['a'])
         q.clear_ordering(True)
         q.set_limits(high=1)
         compiler = q.get_compiler(using=using)
-        return bool(compiler.execute_sql(SINGLE))
+        return compiler.has_results()
 
     def combine(self, rhs, connector):
         """
@@ -615,7 +613,6 @@ class Query(object):
             for model, values in six.iteritems(seen):
                 callback(target, model, values)
 
-
     def deferred_to_columns_cb(self, target, model, fields):
         """
         Callback used by deferred_to_columns(). The "target" parameter should
@@ -627,7 +624,6 @@ class Query(object):
         for field in fields:
             target[table].add(field.column)
 
-
     def table_alias(self, table_name, create=False):
         """
         Returns a table alias for the given table_name and whether this is a
@@ -955,7 +951,6 @@ class Query(object):
                 self.unref_alias(alias)
         self.included_inherited_models = {}
 
-
     def add_aggregate(self, aggregate, model, alias, is_summary):
         """
         Adds a single aggregate expression to the Query
@@ -1780,7 +1775,7 @@ class Query(object):
             return self._aggregate_select_cache
         elif self.aggregate_select_mask is not None:
             self._aggregate_select_cache = SortedDict([
-                (k,v) for k,v in self.aggregates.items()
+                (k, v) for k, v in self.aggregates.items()
                 if k in self.aggregate_select_mask
             ])
             return self._aggregate_select_cache
@@ -1793,7 +1788,7 @@ class Query(object):
             return self._extra_select_cache
         elif self.extra_select_mask is not None:
             self._extra_select_cache = SortedDict([
-                (k,v) for k,v in self.extra.items()
+                (k, v) for k, v in self.extra.items()
                 if k in self.extra_select_mask
             ])
             return self._extra_select_cache
@@ -1876,6 +1871,7 @@ class Query(object):
         else:
             return field.null
 
+
 def get_order_dir(field, default='ASC'):
     """
     Returns the field name and direction for an order specification. For
@@ -1900,6 +1896,7 @@ def add_to_dict(data, key, value):
     else:
         data[key] = set([value])
 
+
 def is_reverse_o2o(field):
     """
     A little helper to check if the given field is reverse-o2o. The field is
@@ -1907,6 +1904,7 @@ def is_reverse_o2o(field):
     """
     return not hasattr(field, 'rel') and field.field.unique
 
+
 def alias_diff(refcounts_before, refcounts_after):
     """
     Given the before and after copies of refcounts works out which aliases
diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index 20770162c9..6aab02bd9a 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -7,7 +7,7 @@ from django.core.exceptions import FieldError
 from django.db import connections
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import DateField, DateTimeField, FieldDoesNotExist
-from django.db.models.sql.constants import *
+from django.db.models.sql.constants import GET_ITERATOR_CHUNK_SIZE, SelectInfo
 from django.db.models.sql.datastructures import Date, DateTime
 from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, Constraint
@@ -20,6 +20,7 @@ from django.utils import timezone
 __all__ = ['DeleteQuery', 'UpdateQuery', 'InsertQuery', 'DateQuery',
         'DateTimeQuery', 'AggregateQuery']
 
+
 class DeleteQuery(Query):
     """
     Delete queries are done through this class, since they are more constrained
@@ -77,7 +78,9 @@ class DeleteQuery(Query):
                 return
             else:
                 innerq.clear_select_clause()
-                innerq.select = [SelectInfo((self.get_initial_alias(), pk.column), None)]
+                innerq.select = [
+                    SelectInfo((self.get_initial_alias(), pk.column), None)
+                ]
                 values = innerq
             where = self.where_class()
             where.add((Constraint(None, pk.column, pk), 'in', values), AND)
@@ -178,6 +181,7 @@ class UpdateQuery(Query):
             result.append(query)
         return result
 
+
 class InsertQuery(Query):
     compiler = 'SQLInsertCompiler'
 
@@ -215,6 +219,7 @@ class InsertQuery(Query):
         self.objs = objs
         self.raw = raw
 
+
 class DateQuery(Query):
     """
     A DateQuery is a normal query, except that it specifically selects a single
@@ -260,6 +265,7 @@ class DateQuery(Query):
     def _get_select(self, col, lookup_type):
         return Date(col, lookup_type)
 
+
 class DateTimeQuery(DateQuery):
     """
     A DateTimeQuery is like a DateQuery but for a datetime field. If time zone
@@ -280,6 +286,7 @@ class DateTimeQuery(DateQuery):
             tzname = timezone._get_timezone_name(self.tzinfo)
         return DateTime(col, lookup_type, tzname)
 
+
 class AggregateQuery(Query):
     """
     An AggregateQuery takes another query as a parameter to the FROM
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 2a342d417a..2e83ecdce4 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -4,6 +4,7 @@ Code to manage the creation and SQL rendering of 'where' constraints.
 
 from __future__ import absolute_import
 
+import collections
 import datetime
 from itertools import repeat
 
@@ -11,15 +12,16 @@ from django.conf import settings
 from django.db.models.fields import DateTimeField, Field
 from django.db.models.sql.datastructures import EmptyResultSet, Empty
 from django.db.models.sql.aggregates import Aggregate
-from django.utils.itercompat import is_iterator
 from django.utils.six.moves import xrange
 from django.utils import timezone
 from django.utils import tree
 
+
 # Connection types
 AND = 'AND'
 OR = 'OR'
 
+
 class EmptyShortCircuit(Exception):
     """
     Internal exception used to indicate that a "matches nothing" node should be
@@ -27,6 +29,7 @@ class EmptyShortCircuit(Exception):
     """
     pass
 
+
 class WhereNode(tree.Node):
     """
     Used to represent the SQL where-clause.
@@ -58,7 +61,7 @@ class WhereNode(tree.Node):
         if not isinstance(data, (list, tuple)):
             return data
         obj, lookup_type, value = data
-        if is_iterator(value):
+        if isinstance(value, collections.Iterator):
             # Consume any generators immediately, so that we can determine
             # emptiness and transform any non-empty values correctly.
             value = list(value)
@@ -175,7 +178,7 @@ class WhereNode(tree.Node):
         """
         lvalue, lookup_type, value_annotation, params_or_value = child
         field_internal_type = lvalue.field.get_internal_type() if lvalue.field else None
-        
+
         if isinstance(lvalue, Constraint):
             try:
                 lvalue, params = lvalue.process(lookup_type, params_or_value, connection)
@@ -304,14 +307,15 @@ class WhereNode(tree.Node):
                 clone.children.append(child)
         return clone
 
-class EmptyWhere(WhereNode):
 
+class EmptyWhere(WhereNode):
     def add(self, data, connector):
         return
 
     def as_sql(self, qn=None, connection=None):
         raise EmptyResultSet
 
+
 class EverythingNode(object):
     """
     A node that matches everything.
@@ -385,6 +389,7 @@ class Constraint(object):
             new.alias, new.col, new.field = change_map[self.alias], self.col, self.field
             return new
 
+
 class SubqueryConstraint(object):
     def __init__(self, alias, columns, targets, query_object):
         self.alias = alias
diff --git a/django/db/transaction.py b/django/db/transaction.py
index 96be981e7b..bb2dbb8e9e 100644
--- a/django/db/transaction.py
+++ b/django/db/transaction.py
@@ -27,6 +27,7 @@ class TransactionManagementError(Exception):
     """
     pass
 
+
 ################
 # Private APIs #
 ################
@@ -40,6 +41,7 @@ def get_connection(using=None):
         using = DEFAULT_DB_ALIAS
     return connections[using]
 
+
 ###########################
 # Deprecated private APIs #
 ###########################
@@ -56,6 +58,7 @@ def abort(using=None):
     """
     get_connection(using).abort()
 
+
 def enter_transaction_management(managed=True, using=None, forced=False):
     """
     Enters transaction management for a running thread. It must be balanced with
@@ -68,6 +71,7 @@ def enter_transaction_management(managed=True, using=None, forced=False):
     """
     get_connection(using).enter_transaction_management(managed, forced)
 
+
 def leave_transaction_management(using=None):
     """
     Leaves transaction management for a running thread. A dirty flag is carried
@@ -76,6 +80,7 @@ def leave_transaction_management(using=None):
     """
     get_connection(using).leave_transaction_management()
 
+
 def is_dirty(using=None):
     """
     Returns True if the current transaction requires a commit for changes to
@@ -83,6 +88,7 @@ def is_dirty(using=None):
     """
     return get_connection(using).is_dirty()
 
+
 def set_dirty(using=None):
     """
     Sets a dirty flag for the current thread and code streak. This can be used
@@ -91,6 +97,7 @@ def set_dirty(using=None):
     """
     get_connection(using).set_dirty()
 
+
 def set_clean(using=None):
     """
     Resets a dirty flag for the current thread and code streak. This can be used
@@ -99,22 +106,27 @@ def set_clean(using=None):
     """
     get_connection(using).set_clean()
 
+
 def is_managed(using=None):
     warnings.warn("'is_managed' is deprecated.",
         DeprecationWarning, stacklevel=2)
 
+
 def managed(flag=True, using=None):
     warnings.warn("'managed' no longer serves a purpose.",
         DeprecationWarning, stacklevel=2)
 
+
 def commit_unless_managed(using=None):
     warnings.warn("'commit_unless_managed' is now a no-op.",
         DeprecationWarning, stacklevel=2)
 
+
 def rollback_unless_managed(using=None):
     warnings.warn("'rollback_unless_managed' is now a no-op.",
         DeprecationWarning, stacklevel=2)
 
+
 ###############
 # Public APIs #
 ###############
@@ -125,24 +137,28 @@ def get_autocommit(using=None):
     """
     return get_connection(using).get_autocommit()
 
+
 def set_autocommit(autocommit, using=None):
     """
     Set the autocommit status of the connection.
     """
     return get_connection(using).set_autocommit(autocommit)
 
+
 def commit(using=None):
     """
     Commits a transaction and resets the dirty flag.
     """
     get_connection(using).commit()
 
+
 def rollback(using=None):
     """
     Rolls back a transaction and resets the dirty flag.
     """
     get_connection(using).rollback()
 
+
 def savepoint(using=None):
     """
     Creates a savepoint (if supported and required by the backend) inside the
@@ -151,6 +167,7 @@ def savepoint(using=None):
     """
     return get_connection(using).savepoint()
 
+
 def savepoint_rollback(sid, using=None):
     """
     Rolls back the most recent savepoint (if one exists). Does nothing if
@@ -158,6 +175,7 @@ def savepoint_rollback(sid, using=None):
     """
     get_connection(using).savepoint_rollback(sid)
 
+
 def savepoint_commit(sid, using=None):
     """
     Commits the most recent savepoint (if one exists). Does nothing if
@@ -165,18 +183,21 @@ def savepoint_commit(sid, using=None):
     """
     get_connection(using).savepoint_commit(sid)
 
+
 def clean_savepoints(using=None):
     """
     Resets the counter used to generate unique savepoint ids in this thread.
     """
     get_connection(using).clean_savepoints()
 
+
 def get_rollback(using=None):
     """
     Gets the "needs rollback" flag -- for *advanced use* only.
     """
     return get_connection(using).get_rollback()
 
+
 def set_rollback(rollback, using=None):
     """
     Sets or unsets the "needs rollback" flag -- for *advanced use* only.
@@ -191,6 +212,7 @@ def set_rollback(rollback, using=None):
     """
     return get_connection(using).set_rollback(rollback)
 
+
 #################################
 # Decorators / context managers #
 #################################
@@ -398,6 +420,7 @@ class Transaction(object):
                 return func(*args, **kwargs)
         return inner
 
+
 def _transaction_func(entering, exiting, using):
     """
     Takes 3 things, an entering function (what to do to start this block of
@@ -436,6 +459,7 @@ def autocommit(using=None):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_on_success(using=None):
     """
     This decorator activates commit on response. This way, if the view function
@@ -466,6 +490,7 @@ def commit_on_success(using=None):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_manually(using=None):
     """
     Decorator that activates manual transaction control. It just disables
@@ -484,6 +509,7 @@ def commit_manually(using=None):
 
     return _transaction_func(entering, exiting, using)
 
+
 def commit_on_success_unless_managed(using=None, savepoint=False):
     """
     Transitory API to preserve backwards-compatibility while refactoring.
diff --git a/django/forms/fields.py b/django/forms/fields.py
index c4bc3fa88c..a794c02e9f 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -370,8 +370,14 @@ class DecimalField(IntegerField):
 
     def widget_attrs(self, widget):
         attrs = super(DecimalField, self).widget_attrs(widget)
-        if isinstance(widget, NumberInput) and self.decimal_places:
-            attrs['step'] = '0.%s1' % ('0' * (self.decimal_places - 1))
+        if isinstance(widget, NumberInput):
+            if self.decimal_places is not None:
+                # Use exponential notation for small values since they might
+                # be parsed as 0 otherwise. ref #20765
+                step = str(Decimal('1') / 10 ** self.decimal_places).lower()
+            else:
+                step = 'any'
+            attrs.setdefault('step', step)
         return attrs
 
 
@@ -1019,7 +1025,7 @@ class MultiValueField(Field):
             if not isinstance(initial, list):
                 initial = self.widget.decompress(initial)
         for field, initial, data in zip(self.fields, initial, data):
-            if field._has_changed(initial, data):
+            if field._has_changed(field.to_python(initial), data):
                 return True
         return False
 
diff --git a/django/forms/forms.py b/django/forms/forms.py
index 6d59271d17..e144eb60f8 100644
--- a/django/forms/forms.py
+++ b/django/forms/forms.py
@@ -77,7 +77,7 @@ class BaseForm(object):
     # information. Any improvements to the form API should be made to *this*
     # class, not to the Form class.
     def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
-                 initial=None, error_class=ErrorList, label_suffix=':',
+                 initial=None, error_class=ErrorList, label_suffix=None,
                  empty_permitted=False):
         self.is_bound = data is not None or files is not None
         self.data = data or {}
@@ -86,7 +86,8 @@ class BaseForm(object):
         self.prefix = prefix
         self.initial = initial or {}
         self.error_class = error_class
-        self.label_suffix = label_suffix
+        # Translators: This is the default suffix added to form field labels
+        self.label_suffix = label_suffix if label_suffix is not None else _(':')
         self.empty_permitted = empty_permitted
         self._errors = None # Stores the errors after clean() has been called.
         self._changed_data = None
@@ -518,7 +519,9 @@ class BoundField(object):
         """
         contents = contents or self.label
         # Only add the suffix if the label does not end in punctuation.
-        if self.form.label_suffix and contents and contents[-1] not in ':?.!':
+        # Translators: If found as last label character, these punctuation
+        # characters will prevent the default label_suffix to be appended to the label
+        if self.form.label_suffix and contents and contents[-1] not in _(':?.!'):
             contents = format_html('{0}{1}', contents, self.form.label_suffix)
         widget = self.field.widget
         id_ = widget.attrs.get('id') or self.auto_id
diff --git a/django/forms/models.py b/django/forms/models.py
index a0c3009d38..1d3bec1635 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -292,7 +292,7 @@ class ModelFormMetaclass(type):
 
 class BaseModelForm(BaseForm):
     def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
-                 initial=None, error_class=ErrorList, label_suffix=':',
+                 initial=None, error_class=ErrorList, label_suffix=None,
                  empty_permitted=False, instance=None):
         opts = self._meta
         if opts.model is None:
diff --git a/django/forms/util.py b/django/forms/util.py
index 0a73320f83..3c7724900a 100644
--- a/django/forms/util.py
+++ b/django/forms/util.py
@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 
+import warnings
+
 from django.conf import settings
 from django.utils.html import format_html, format_html_join
 from django.utils.encoding import force_text, python_2_unicode_compatible
@@ -21,6 +23,11 @@ def flatatt(attrs):
 
     The result is passed through 'mark_safe'.
     """
+    if [v for v in attrs.values() if v is True or v is False]:
+        warnings.warn(
+            'The meaning of boolean values for widget attributes will change in Django 1.8',
+            DeprecationWarning
+        )
     return format_html_join('', ' {0}="{1}"', sorted(attrs.items()))
 
 @python_2_unicode_compatible
diff --git a/django/http/multipartparser.py b/django/http/multipartparser.py
index eeb435fa57..9a5193e49b 100644
--- a/django/http/multipartparser.py
+++ b/django/http/multipartparser.py
@@ -50,7 +50,7 @@ class MultiPartParser(object):
             The raw post data, as a file-like object.
         :upload_handlers:
             A list of UploadHandler instances that perform operations on the uploaded
-            data. 
+            data.
         :encoding:
             The encoding with which to treat the incoming data.
         """
@@ -177,11 +177,9 @@ class MultiPartParser(object):
                     file_name = force_text(file_name, encoding, errors='replace')
                     file_name = self.IE_sanitize(unescape_entities(file_name))
 
-                    content_type = meta_data.get('content-type', ('',))[0].strip()
-                    try:
-                        charset = meta_data.get('content-type', (0, {}))[1].get('charset', None)
-                    except:
-                        charset = None
+                    content_type, content_type_extra = meta_data.get('content-type', ('', {}))
+                    content_type = content_type.strip()
+                    charset = content_type_extra.get('charset')
 
                     try:
                         content_length = int(meta_data.get('content-length')[0])
@@ -194,7 +192,7 @@ class MultiPartParser(object):
                             try:
                                 handler.new_file(field_name, file_name,
                                                  content_type, content_length,
-                                                 charset)
+                                                 charset, content_type_extra)
                             except StopFutureHandlers:
                                 break
 
diff --git a/django/template/context.py b/django/template/context.py
index 1ef7e889bc..3830c1c660 100644
--- a/django/template/context.py
+++ b/django/template/context.py
@@ -12,6 +12,21 @@ class ContextPopException(Exception):
     "pop() has been called more times than push()"
     pass
 
+
+class ContextDict(dict):
+    def __init__(self, context, *args, **kwargs):
+        super(ContextDict, self).__init__(*args, **kwargs)
+
+        context.dicts.append(self)
+        self.context = context
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args, **kwargs):
+        self.context.pop()
+
+
 class BaseContext(object):
     def __init__(self, dict_=None):
         self._reset_dicts(dict_)
@@ -34,10 +49,8 @@ class BaseContext(object):
         for d in reversed(self.dicts):
             yield d
 
-    def push(self):
-        d = {}
-        self.dicts.append(d)
-        return d
+    def push(self, *args, **kwargs):
+        return ContextDict(self, *args, **kwargs)
 
     def pop(self):
         if len(self.dicts) == 1:
@@ -83,6 +96,7 @@ class BaseContext(object):
         new_context._reset_dicts(values)
         return new_context
 
+
 class Context(BaseContext):
     "A stack container for variable context"
     def __init__(self, dict_=None, autoescape=True, current_app=None,
@@ -106,6 +120,7 @@ class Context(BaseContext):
         self.dicts.append(other_dict)
         return other_dict
 
+
 class RenderContext(BaseContext):
     """
     A stack container for storing Template state.
diff --git a/django/template/defaulttags.py b/django/template/defaulttags.py
index 5b2a1b9501..5c9490f749 100644
--- a/django/template/defaulttags.py
+++ b/django/template/defaulttags.py
@@ -95,10 +95,9 @@ class FilterNode(Node):
     def render(self, context):
         output = self.nodelist.render(context)
         # Apply filters.
-        context.update({'var': output})
-        filtered = self.filter_expr.resolve(context)
-        context.pop()
-        return filtered
+        with context.push(var=output):
+            return self.filter_expr.resolve(context)
+
 
 class FirstOfNode(Node):
     def __init__(self, variables, escape=False):
@@ -143,71 +142,69 @@ class ForNode(Node):
             parentloop = context['forloop']
         else:
             parentloop = {}
-        context.push()
-        try:
-            values = self.sequence.resolve(context, True)
-        except VariableDoesNotExist:
-            values = []
-        if values is None:
-            values = []
-        if not hasattr(values, '__len__'):
-            values = list(values)
-        len_values = len(values)
-        if len_values < 1:
-            context.pop()
-            return self.nodelist_empty.render(context)
-        nodelist = NodeList()
-        if self.is_reversed:
-            values = reversed(values)
-        unpack = len(self.loopvars) > 1
-        # Create a forloop value in the context.  We'll update counters on each
-        # iteration just below.
-        loop_dict = context['forloop'] = {'parentloop': parentloop}
-        for i, item in enumerate(values):
-            # Shortcuts for current loop iteration number.
-            loop_dict['counter0'] = i
-            loop_dict['counter'] = i+1
-            # Reverse counter iteration numbers.
-            loop_dict['revcounter'] = len_values - i
-            loop_dict['revcounter0'] = len_values - i - 1
-            # Boolean values designating first and last times through loop.
-            loop_dict['first'] = (i == 0)
-            loop_dict['last'] = (i == len_values - 1)
+        with context.push():
+            try:
+                values = self.sequence.resolve(context, True)
+            except VariableDoesNotExist:
+                values = []
+            if values is None:
+                values = []
+            if not hasattr(values, '__len__'):
+                values = list(values)
+            len_values = len(values)
+            if len_values < 1:
+                return self.nodelist_empty.render(context)
+            nodelist = NodeList()
+            if self.is_reversed:
+                values = reversed(values)
+            unpack = len(self.loopvars) > 1
+            # Create a forloop value in the context.  We'll update counters on each
+            # iteration just below.
+            loop_dict = context['forloop'] = {'parentloop': parentloop}
+            for i, item in enumerate(values):
+                # Shortcuts for current loop iteration number.
+                loop_dict['counter0'] = i
+                loop_dict['counter'] = i+1
+                # Reverse counter iteration numbers.
+                loop_dict['revcounter'] = len_values - i
+                loop_dict['revcounter0'] = len_values - i - 1
+                # Boolean values designating first and last times through loop.
+                loop_dict['first'] = (i == 0)
+                loop_dict['last'] = (i == len_values - 1)
 
-            pop_context = False
-            if unpack:
-                # If there are multiple loop variables, unpack the item into
-                # them.
-                try:
-                    unpacked_vars = dict(zip(self.loopvars, item))
-                except TypeError:
-                    pass
-                else:
-                    pop_context = True
-                    context.update(unpacked_vars)
-            else:
-                context[self.loopvars[0]] = item
-            # In TEMPLATE_DEBUG mode provide source of the node which
-            # actually raised the exception
-            if settings.TEMPLATE_DEBUG:
-                for node in self.nodelist_loop:
+                pop_context = False
+                if unpack:
+                    # If there are multiple loop variables, unpack the item into
+                    # them.
                     try:
+                        unpacked_vars = dict(zip(self.loopvars, item))
+                    except TypeError:
+                        pass
+                    else:
+                        pop_context = True
+                        context.update(unpacked_vars)
+                else:
+                    context[self.loopvars[0]] = item
+                # In TEMPLATE_DEBUG mode provide source of the node which
+                # actually raised the exception
+                if settings.TEMPLATE_DEBUG:
+                    for node in self.nodelist_loop:
+                        try:
+                            nodelist.append(node.render(context))
+                        except Exception as e:
+                            if not hasattr(e, 'django_template_source'):
+                                e.django_template_source = node.source
+                            raise
+                else:
+                    for node in self.nodelist_loop:
                         nodelist.append(node.render(context))
-                    except Exception as e:
-                        if not hasattr(e, 'django_template_source'):
-                            e.django_template_source = node.source
-                        raise
-            else:
-                for node in self.nodelist_loop:
-                    nodelist.append(node.render(context))
-            if pop_context:
-                # The loop variables were pushed on to the context so pop them
-                # off again. This is necessary because the tag lets the length
-                # of loopvars differ to the length of each set of items and we
-                # don't want to leave any vars from the previous loop on the
-                # context.
-                context.pop()
-        context.pop()
+                if pop_context:
+                    # The loop variables were pushed on to the context so pop them
+                    # off again. This is necessary because the tag lets the length
+                    # of loopvars differ to the length of each set of items and we
+                    # don't want to leave any vars from the previous loop on the
+                    # context.
+                    context.pop()
         return nodelist.render(context)
 
 class IfChangedNode(Node):
@@ -500,10 +497,9 @@ class WithNode(Node):
     def render(self, context):
         values = dict([(key, val.resolve(context)) for key, val in
                        six.iteritems(self.extra_context)])
-        context.update(values)
-        output = self.nodelist.render(context)
-        context.pop()
-        return output
+        with context.push(**values):
+            return self.nodelist.render(context)
+
 
 @register.tag
 def autoescape(parser, token):
diff --git a/django/template/loader.py b/django/template/loader.py
index 6df4e43c4f..44b8f600fb 100644
--- a/django/template/loader.py
+++ b/django/template/loader.py
@@ -164,11 +164,8 @@ def render_to_string(template_name, dictionary=None, context_instance=None):
         return t.render(Context(dictionary))
     # Add the dictionary to the context stack, ensuring it gets removed again
     # to keep the context_instance in the same state it started in.
-    context_instance.update(dictionary)
-    try:
+    with context_instance.push(dictionary):
         return t.render(context_instance)
-    finally:
-        context_instance.pop()
 
 def select_template(template_name_list):
     "Given a list of template names, returns the first that can be loaded."
diff --git a/django/template/loader_tags.py b/django/template/loader_tags.py
index 767f0e5ff8..406775da9d 100644
--- a/django/template/loader_tags.py
+++ b/django/template/loader_tags.py
@@ -47,22 +47,21 @@ class BlockNode(Node):
 
     def render(self, context):
         block_context = context.render_context.get(BLOCK_CONTEXT_KEY)
-        context.push()
-        if block_context is None:
-            context['block'] = self
-            result = self.nodelist.render(context)
-        else:
-            push = block = block_context.pop(self.name)
-            if block is None:
-                block = self
-            # Create new block so we can store context without thread-safety issues.
-            block = BlockNode(block.name, block.nodelist)
-            block.context = context
-            context['block'] = block
-            result = block.nodelist.render(context)
-            if push is not None:
-                block_context.push(self.name, push)
-        context.pop()
+        with context.push():
+            if block_context is None:
+                context['block'] = self
+                result = self.nodelist.render(context)
+            else:
+                push = block = block_context.pop(self.name)
+                if block is None:
+                    block = self
+                # Create new block so we can store context without thread-safety issues.
+                block = BlockNode(block.name, block.nodelist)
+                block.context = context
+                context['block'] = block
+                result = block.nodelist.render(context)
+                if push is not None:
+                    block_context.push(self.name, push)
         return result
 
     def super(self):
@@ -133,10 +132,9 @@ class BaseIncludeNode(Node):
                        in six.iteritems(self.extra_context)])
         if self.isolated_context:
             return template.render(context.new(values))
-        context.update(values)
-        output = template.render(context)
-        context.pop()
-        return output
+        with context.push(**values):
+            return template.render(context)
+
 
 class ConstantIncludeNode(BaseIncludeNode):
     def __init__(self, template_path, *args, **kwargs):
diff --git a/django/test/client.py b/django/test/client.py
index 94cfada725..8dbd33ccf1 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -180,7 +180,11 @@ def encode_multipart(boundary, data):
 
 def encode_file(boundary, key, file):
     to_bytes = lambda s: force_bytes(s, settings.DEFAULT_CHARSET)
-    content_type = mimetypes.guess_type(file.name)[0]
+    if hasattr(file, 'content_type'):
+        content_type = file.content_type
+    else:
+        content_type = mimetypes.guess_type(file.name)[0]
+
     if content_type is None:
         content_type = 'application/octet-stream'
     return [
diff --git a/django/test/runner.py b/django/test/runner.py
index 6897906098..c7881ada63 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -238,6 +238,7 @@ def setup_databases(verbosity, interactive, **kwargs):
     mirrored_aliases = {}
     test_databases = {}
     dependencies = {}
+    default_sig = connections[DEFAULT_DB_ALIAS].creation.test_db_signature()
     for alias in connections:
         connection = connections[alias]
         if connection.settings_dict['TEST_MIRROR']:
@@ -259,7 +260,7 @@ def setup_databases(verbosity, interactive, **kwargs):
                 dependencies[alias] = (
                     connection.settings_dict['TEST_DEPENDENCIES'])
             else:
-                if alias != DEFAULT_DB_ALIAS:
+                if alias != DEFAULT_DB_ALIAS and connection.creation.test_db_signature() != default_sig:
                     dependencies[alias] = connection.settings_dict.get(
                         'TEST_DEPENDENCIES', [DEFAULT_DB_ALIAS])
 
@@ -271,15 +272,16 @@ def setup_databases(verbosity, interactive, **kwargs):
         test_databases.items(), dependencies):
         test_db_name = None
         # Actually create the database for the first connection
-
         for alias in aliases:
             connection = connections[alias]
-            old_names.append((connection, db_name, True))
             if test_db_name is None:
                 test_db_name = connection.creation.create_test_db(
                         verbosity, autoclobber=not interactive)
+                destroy = True
             else:
                 connection.settings_dict['NAME'] = test_db_name
+                destroy = False
+            old_names.append((connection, db_name, destroy))
 
     for alias, mirror_alias in mirrored_aliases.items():
         mirrors.append((alias, connections[alias].settings_dict['NAME']))
diff --git a/django/test/signals.py b/django/test/signals.py
index a96bdff3b3..de8802b381 100644
--- a/django/test/signals.py
+++ b/django/test/signals.py
@@ -1,5 +1,6 @@
 import os
 import time
+import warnings
 
 from django.conf import settings
 from django.db import connections
@@ -9,11 +10,14 @@ from django.utils.functional import empty
 
 template_rendered = Signal(providing_args=["template", "context"])
 
-setting_changed = Signal(providing_args=["setting", "value"])
+setting_changed = Signal(providing_args=["setting", "value", "enter"])
 
 # Most setting_changed receivers are supposed to be added below,
 # except for cases where the receiver is related to a contrib app.
 
+# Settings that may not work well when using 'override_settings' (#19031)
+COMPLEX_OVERRIDE_SETTINGS = set(['DATABASES'])
+
 
 @receiver(setting_changed)
 def update_connections_time_zone(**kwargs):
@@ -74,8 +78,15 @@ def language_changed(**kwargs):
         if kwargs['setting'] == 'LOCALE_PATHS':
             trans_real._translations = {}
 
+
 @receiver(setting_changed)
 def file_storage_changed(**kwargs):
     if kwargs['setting'] in ('MEDIA_ROOT', 'DEFAULT_FILE_STORAGE'):
         from django.core.files.storage import default_storage
         default_storage._wrapped = empty
+
+
+@receiver(setting_changed)
+def complex_setting_changed(**kwargs):
+    if kwargs['enter'] and kwargs['setting'] in COMPLEX_OVERRIDE_SETTINGS:
+        warnings.warn("Overriding setting %s can lead to unexpected behaviour." % kwargs['setting'])
diff --git a/django/test/testcases.py b/django/test/testcases.py
index c5299bdabc..6f3f1c00e4 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -8,7 +8,6 @@ import json
 import os
 import re
 import sys
-import select
 import socket
 import threading
 import unittest
@@ -880,10 +879,19 @@ class TestCase(TransactionTestCase):
             self.atomics[db_name].__exit__(None, None, None)
 
 
+class CheckCondition(object):
+    """Descriptor class for deferred condition checking"""
+    def __init__(self, cond_func):
+        self.cond_func = cond_func
+
+    def __get__(self, obj, objtype):
+        return self.cond_func()
+
+
 def _deferredSkip(condition, reason):
     def decorator(test_func):
         if not (isinstance(test_func, type) and
-                issubclass(test_func, TestCase)):
+                issubclass(test_func, unittest.TestCase)):
             @wraps(test_func)
             def skip_wrapper(*args, **kwargs):
                 if condition():
@@ -891,7 +899,9 @@ def _deferredSkip(condition, reason):
                 return test_func(*args, **kwargs)
             test_item = skip_wrapper
         else:
+            # Assume a class is decorated
             test_item = test_func
+            test_item.__unittest_skip__ = CheckCondition(condition)
         test_item.__unittest_skip_why__ = reason
         return test_item
     return decorator
@@ -924,104 +934,6 @@ class QuietWSGIRequestHandler(WSGIRequestHandler):
         pass
 
 
-if sys.version_info >= (3, 3, 0):
-    _ImprovedEvent = threading.Event
-elif sys.version_info >= (2, 7, 0):
-    _ImprovedEvent = threading._Event
-else:
-    class _ImprovedEvent(threading._Event):
-        """
-        Does the same as `threading.Event` except it overrides the wait() method
-        with some code borrowed from Python 2.7 to return the set state of the
-        event (see: http://hg.python.org/cpython/rev/b5aa8aa78c0f/). This allows
-        to know whether the wait() method exited normally or because of the
-        timeout. This class can be removed when Django supports only Python >= 2.7.
-        """
-
-        def wait(self, timeout=None):
-            self._Event__cond.acquire()
-            try:
-                if not self._Event__flag:
-                    self._Event__cond.wait(timeout)
-                return self._Event__flag
-            finally:
-                self._Event__cond.release()
-
-
-class StoppableWSGIServer(WSGIServer):
-    """
-    The code in this class is borrowed from the `SocketServer.BaseServer` class
-    in Python 2.6. The important functionality here is that the server is non-
-    blocking and that it can be shut down at any moment. This is made possible
-    by the server regularly polling the socket and checking if it has been
-    asked to stop.
-    Note for the future: Once Django stops supporting Python 2.6, this class
-    can be removed as `WSGIServer` will have this ability to shutdown on
-    demand and will not require the use of the _ImprovedEvent class whose code
-    is borrowed from Python 2.7.
-    """
-
-    def __init__(self, *args, **kwargs):
-        super(StoppableWSGIServer, self).__init__(*args, **kwargs)
-        self.__is_shut_down = _ImprovedEvent()
-        self.__serving = False
-
-    def serve_forever(self, poll_interval=0.5):
-        """
-        Handle one request at a time until shutdown.
-
-        Polls for shutdown every poll_interval seconds.
-        """
-        self.__serving = True
-        self.__is_shut_down.clear()
-        while self.__serving:
-            r, w, e = select.select([self], [], [], poll_interval)
-            if r:
-                self._handle_request_noblock()
-        self.__is_shut_down.set()
-
-    def shutdown(self):
-        """
-        Stops the serve_forever loop.
-
-        Blocks until the loop has finished. This must be called while
-        serve_forever() is running in another thread, or it will
-        deadlock.
-        """
-        self.__serving = False
-        if not self.__is_shut_down.wait(2):
-            raise RuntimeError(
-                "Failed to shutdown the live test server in 2 seconds. The "
-                "server might be stuck or generating a slow response.")
-
-    def handle_request(self):
-        """Handle one request, possibly blocking.
-        """
-        fd_sets = select.select([self], [], [], None)
-        if not fd_sets[0]:
-            return
-        self._handle_request_noblock()
-
-    def _handle_request_noblock(self):
-        """
-        Handle one request, without blocking.
-
-        I assume that select.select has returned that the socket is
-        readable before this function was called, so there should be
-        no risk of blocking in get_request().
-        """
-        try:
-            request, client_address = self.get_request()
-        except socket.error:
-            return
-        if self.verify_request(request, client_address):
-            try:
-                self.process_request(request, client_address)
-            except Exception:
-                self.handle_error(request, client_address)
-                self.close_request(request)
-
-
 class _MediaFilesHandler(StaticFilesHandler):
     """
     Handler for serving the media files. This is a private class that is
@@ -1071,7 +983,7 @@ class LiveServerThread(threading.Thread):
             # one that is free to use for the WSGI server.
             for index, port in enumerate(self.possible_ports):
                 try:
-                    self.httpd = StoppableWSGIServer(
+                    self.httpd = WSGIServer(
                         (self.host, port), QuietWSGIRequestHandler)
                 except WSGIServerException as e:
                     if (index + 1 < len(self.possible_ports) and
@@ -1128,7 +1040,7 @@ class LiveServerTestCase(TransactionTestCase):
         for conn in connections.all():
             # If using in-memory sqlite databases, pass the connections to
             # the server thread.
-            if (conn.settings_dict['ENGINE'].rsplit('.', 1)[-1] in ('sqlite3', 'spatialite')
+            if (conn.vendor == 'sqlite'
                 and conn.settings_dict['NAME'] == ':memory:'):
                 # Explicitly enable thread-shareability for this connection
                 conn.allow_thread_sharing = True
@@ -1180,7 +1092,7 @@ class LiveServerTestCase(TransactionTestCase):
 
         # Restore sqlite connections' non-sharability
         for conn in connections.all():
-            if (conn.settings_dict['ENGINE'].rsplit('.', 1)[-1] in ('sqlite3', 'spatialite')
+            if (conn.vendor == 'sqlite'
                 and conn.settings_dict['NAME'] == ':memory:'):
                 conn.allow_thread_sharing = False
 
diff --git a/django/test/utils.py b/django/test/utils.py
index 70ce640239..dc3e5952ea 100644
--- a/django/test/utils.py
+++ b/django/test/utils.py
@@ -228,7 +228,7 @@ class override_settings(object):
         settings._wrapped = override
         for key, new_value in self.options.items():
             setting_changed.send(sender=settings._wrapped.__class__,
-                                 setting=key, value=new_value)
+                                 setting=key, value=new_value, enter=True)
 
     def disable(self):
         settings._wrapped = self.wrapped
@@ -236,7 +236,7 @@ class override_settings(object):
         for key in self.options:
             new_value = getattr(settings, key, None)
             setting_changed.send(sender=settings._wrapped.__class__,
-                                 setting=key, value=new_value)
+                                 setting=key, value=new_value, enter=False)
 
 
 def compare_xml(want, got):
diff --git a/django/utils/feedgenerator.py b/django/utils/feedgenerator.py
index 7eba842a89..de32b9f8cc 100644
--- a/django/utils/feedgenerator.py
+++ b/django/utils/feedgenerator.py
@@ -114,11 +114,11 @@ class SyndicationFeed(object):
     def add_item(self, title, link, description, author_email=None,
         author_name=None, author_link=None, pubdate=None, comments=None,
         unique_id=None, unique_id_is_permalink=None, enclosure=None,
-        categories=(), item_copyright=None, ttl=None, **kwargs):
+        categories=(), item_copyright=None, ttl=None, updateddate=None, **kwargs):
         """
         Adds an item to the feed. All args are expected to be Python Unicode
-        objects except pubdate, which is a datetime.datetime object, and
-        enclosure, which is an instance of the Enclosure class.
+        objects except pubdate and updateddate, which are datetime.datetime
+        objects, and enclosure, which is an instance of the Enclosure class.
         """
         to_unicode = lambda s: force_text(s, strings_only=True)
         if categories:
@@ -134,6 +134,7 @@ class SyndicationFeed(object):
             'author_name': to_unicode(author_name),
             'author_link': iri_to_uri(author_link),
             'pubdate': pubdate,
+            'updateddate': updateddate,
             'comments': to_unicode(comments),
             'unique_id': to_unicode(unique_id),
             'unique_id_is_permalink': unique_id_is_permalink,
@@ -191,15 +192,20 @@ class SyndicationFeed(object):
 
     def latest_post_date(self):
         """
-        Returns the latest item's pubdate. If none of them have a pubdate,
-        this returns the current date/time.
+        Returns the latest item's pubdate or updateddate. If no items
+        have either of these attributes this returns the current date/time.
         """
-        updates = [i['pubdate'] for i in self.items if i['pubdate'] is not None]
-        if len(updates) > 0:
-            updates.sort()
-            return updates[-1]
-        else:
-            return datetime.datetime.now()
+        latest_date = None
+        date_keys = ('updateddate', 'pubdate')
+
+        for item in self.items:
+            for date_key in date_keys:
+                item_date = item.get(date_key)
+                if item_date:
+                    if latest_date is None or item_date > latest_date:
+                        latest_date = item_date
+
+        return latest_date or datetime.datetime.now()
 
 class Enclosure(object):
     "Represents an RSS enclosure"
@@ -349,8 +355,12 @@ class Atom1Feed(SyndicationFeed):
     def add_item_elements(self, handler, item):
         handler.addQuickElement("title", item['title'])
         handler.addQuickElement("link", "", {"href": item['link'], "rel": "alternate"})
+
         if item['pubdate'] is not None:
-            handler.addQuickElement("updated", rfc3339_date(item['pubdate']))
+            handler.addQuickElement('published', rfc3339_date(item['pubdate']))
+
+        if item['updateddate'] is not None:
+            handler.addQuickElement('updated', rfc3339_date(item['updateddate']))
 
         # Author information.
         if item['author_name'] is not None:
diff --git a/django/utils/functional.py b/django/utils/functional.py
index 0606c775ef..e23bd3ff80 100644
--- a/django/utils/functional.py
+++ b/django/utils/functional.py
@@ -403,9 +403,8 @@ def partition(predicate, values):
 if sys.version_info >= (2, 7, 2):
     from functools import total_ordering
 else:
-    # For Python < 2.7.2. Python 2.6 does not have total_ordering, and
-    # total_ordering in 2.7 versions prior to 2.7.2 is buggy. See
-    # http://bugs.python.org/issue10042 for details. For these versions use
+    # For Python < 2.7.2. total_ordering in versions prior to 2.7.2 is buggy.
+    # See http://bugs.python.org/issue10042 for details. For these versions use
     # code borrowed from Python 2.7.3.
     def total_ordering(cls):
         """Class decorator that fills in missing ordering methods"""
diff --git a/django/utils/image.py b/django/utils/image.py
index 2fd0c6e6b0..dd2fab6197 100644
--- a/django/utils/image.py
+++ b/django/utils/image.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 """
 To provide a shim layer over Pillow/PIL situation until the PIL support is
-removed.
+removed. See #19934.
 
 
 Combinations To Account For
@@ -132,6 +132,8 @@ def _detect_image_library():
     try:
         from PIL import ImageFile as PILImageFile
     except ImportError:
+        # This import cannot fail unless Pillow/PIL install is completely
+        # broken (e.g. missing Python modules).
         import ImageFile as PILImageFile
 
     # Finally, warn about deprecation...
diff --git a/django/utils/itercompat.py b/django/utils/itercompat.py
index 1df1e57cb2..096f808671 100644
--- a/django/utils/itercompat.py
+++ b/django/utils/itercompat.py
@@ -4,9 +4,6 @@ Where possible, we try to use the system-native version and only fall back to
 these implementations if necessary.
 """
 
-import collections
-import sys
-
 
 def is_iterable(x):
     "A implementation independent way of checking for iterables"
@@ -16,14 +13,3 @@ def is_iterable(x):
         return False
     else:
         return True
-
-def is_iterator(x):
-    """An implementation independent way of checking for iterators
-
-    Python 2.6 has a different implementation of collections.Iterator which
-    accepts anything with a `next` method. 2.7+ requires and `__iter__` method
-    as well.
-    """
-    if sys.version_info >= (2, 7):
-        return isinstance(x, collections.Iterator)
-    return isinstance(x, collections.Iterator) and hasattr(x, '__iter__')
diff --git a/django/utils/timesince.py b/django/utils/timesince.py
index 46c387f262..8fb0f64e09 100644
--- a/django/utils/timesince.py
+++ b/django/utils/timesince.py
@@ -17,7 +17,8 @@ def timesince(d, now=None, reversed=False):
     displayed.  For example, "2 weeks, 3 days" and "1 year, 3 months" are
     possible outputs, but "2 weeks, 3 hours" and "1 year, 5 days" are not.
 
-    Adapted from http://blog.natbat.co.uk/archive/2003/Jun/14/time_since
+    Adapted from
+    http://web.archive.org/web/20060617175230/http://blog.natbat.co.uk/archive/2003/Jun/14/time_since
     """
     chunks = (
         (60 * 60 * 24 * 365, ungettext_lazy('%d year', '%d years')),