Added django.newforms -- work-in-progress of the new framework for forms/validators/manipulators

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3944 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 869 insertions, 0 deletions

diff --git a/django/newforms/__init__.py b/django/newforms/__init__.py
new file mode 100644
index 0000000000..1e92027b16
--- /dev/null
+++ b/django/newforms/__init__.py
@@ -0,0 +1,869 @@
+"""
+Django validation and HTML form handling.
+
+TODO:
+    Validation not tied to a particular field
+    <select> and validation of lists
+    Default value for field
+    Field labels
+    Nestable Forms
+    FatalValidationError -- short-circuits all other validators on a form
+    ValidationWarning
+    "This form field requires foo.js" and form.js_includes()
+
+# Form ########################################################################
+
+>>> class Person(Form):
+...     first_name = CharField()
+...     last_name = CharField()
+...     birthday = DateField()
+>>> p = Person({'first_name': u'John', 'last_name': u'Lennon', 'birthday': u'1940-10-9'})
+>>> p.errors()
+{}
+>>> p.is_valid()
+True
+>>> p.errors().as_ul()
+u''
+>>> p.errors().as_text()
+u''
+>>> p.to_python()
+{'first_name': u'John', 'last_name': u'Lennon', 'birthday': datetime.date(1940, 10, 9)}
+>>> print p['first_name']
+<input type="text" name="first_name" value="John" />
+>>> print p['last_name']
+<input type="text" name="last_name" value="Lennon" />
+>>> print p['birthday']
+<input type="text" name="birthday" value="1940-10-09" />
+>>> for boundfield in p:
+...     print boundfield
+<input type="text" name="first_name" value="John" />
+<input type="text" name="last_name" value="Lennon" />
+<input type="text" name="birthday" value="1940-10-09" />
+
+>>> p = Person({'last_name': u'Lennon'})
+>>> p.errors()
+{'first_name': [u'This field is required.'], 'birthday': [u'This field is required.']}
+>>> p.is_valid()
+False
+>>> p.errors().as_ul()
+u'<ul class="errorlist"><li>first_name<ul class="errorlist"><li>This field is required.</li></ul></li><li>birthday<ul class="errorlist"><li>This field is required.</li></ul></li></ul>'
+>>> print p.errors().as_text()
+* first_name
+  * This field is required.
+* birthday
+  * This field is required.
+>>> p.to_python()
+>>> repr(p.to_python())
+'None'
+>>> p['first_name'].errors
+[u'This field is required.']
+>>> p['first_name'].errors.as_ul()
+u'<ul class="errorlist"><li>This field is required.</li></ul>'
+>>> p['first_name'].errors.as_text()
+u'* This field is required.'
+
+>>> p = Person()
+>>> print p['first_name']
+<input type="text" name="first_name" />
+>>> print p['last_name']
+<input type="text" name="last_name" />
+>>> print p['birthday']
+<input type="text" name="birthday" />
+
+>>> class SignupForm(Form):
+...     email = EmailField()
+...     get_spam = BooleanField()
+>>> f = SignupForm()
+>>> print f['email']
+<input type="text" name="email" />
+>>> print f['get_spam']
+<input type="checkbox" name="get_spam" />
+
+>>> f = SignupForm({'email': 'test@example.com', 'get_spam': True})
+>>> print f['email']
+<input type="text" name="email" value="test@example.com" />
+>>> print f['get_spam']
+<input checked="checked" type="checkbox" name="get_spam" />
+
+Any Field can have a Widget class passed to its constructor:
+>>> class ContactForm(Form):
+...     subject = CharField()
+...     message = CharField(widget=Textarea)
+>>> f = ContactForm()
+>>> print f['subject']
+<input type="text" name="subject" />
+>>> print f['message']
+<textarea name="message"></textarea>
+
+as_textarea() and as_text() are shortcuts for changing the output widget type:
+>>> f['subject'].as_textarea()
+u'<textarea name="subject"></textarea>'
+>>> f['message'].as_text()
+u'<input type="text" name="message" />'
+
+The 'widget' parameter to a Field can also be an instance:
+>>> class ContactForm(Form):
+...     subject = CharField()
+...     message = CharField(widget=Textarea(attrs={'rows': 80, 'cols': 20}))
+>>> f = ContactForm()
+>>> print f['message']
+<textarea rows="80" cols="20" name="message"></textarea>
+
+Instance-level attrs are *not* carried over to as_textarea() and as_text():
+>>> f['message'].as_text()
+u'<input type="text" name="message" />'
+>>> f = ContactForm({'subject': 'Hello', 'message': 'I love you.'})
+>>> f['subject'].as_textarea()
+u'<textarea name="subject">Hello</textarea>'
+>>> f['message'].as_text()
+u'<input type="text" name="message" value="I love you." />'
+"""
+
+from django.utils.html import escape
+import datetime
+import re
+import time
+
+# Default encoding for input byte strings.
+DEFAULT_ENCODING = 'utf-8' # TODO: First look at django.conf.settings, then fall back to this.
+
+def smart_unicode(s):
+    if not isinstance(s, unicode):
+        s = unicode(s, DEFAULT_ENCODING)
+    return s
+
+###################
+# VALIDATOR STUFF #
+###################
+
+class ErrorDict(dict):
+    """
+    A collection of errors that knows how to display itself in various formats.
+
+    The dictionary keys are the field names, and the values are the errors.
+    """
+    def __str__(self):
+        return self.as_ul()
+
+    def as_ul(self):
+        if not self: return u''
+        return u'<ul class="errorlist">%s</ul>' % ''.join([u'<li>%s%s</li>' % (k, v) for k, v in self.items()])
+
+    def as_text(self):
+        return u'\n'.join([u'* %s\n%s' % (k, u'\n'.join([u'  * %s' % i for i in v])) for k, v in self.items()])
+
+class ErrorList(list):
+    """
+    A collection of errors that knows how to display itself in various formats.
+    """
+    def __str__(self):
+        return self.as_ul()
+
+    def as_ul(self):
+        if not self: return u''
+        return u'<ul class="errorlist">%s</ul>' % ''.join([u'<li>%s</li>' % e for e in self])
+
+    def as_text(self):
+        if not self: return u''
+        return u'\n'.join([u'* %s' % e for e in self])
+
+class ValidationError(Exception):
+    def __init__(self, message):
+        "ValidationError can be passed a string or a list."
+        if isinstance(message, list):
+            self.messages = ErrorList([smart_unicode(msg) for msg in message])
+        else:
+            assert isinstance(message, basestring), ("%s should be a basestring" % repr(message))
+            message = smart_unicode(message)
+            self.messages = ErrorList([message])
+
+    def __str__(self):
+        # This is needed because, without a __str__(), printing an exception
+        # instance would result in this:
+        # AttributeError: ValidationError instance has no attribute 'args'
+        # See http://www.python.org/doc/current/tut/node10.html#handling
+        return repr(self.messages)
+
+################
+# HTML WIDGETS #
+################
+
+# Converts a dictionary to a single string with key="value", XML-style.
+# Assumes keys do not need to be XML-escaped.
+flatatt = lambda attrs: ' '.join(['%s="%s"' % (k, escape(v)) for k, v in attrs.items()])
+
+class Widget(object):
+    def __init__(self, attrs=None):
+        self.attrs = attrs or {}
+
+    def render(self, name, value):
+        raise NotImplementedError
+
+class TextInput(Widget):
+    """
+    >>> w = TextInput()
+    >>> w.render('email', '')
+    u'<input type="text" name="email" />'
+    >>> w.render('email', None)
+    u'<input type="text" name="email" />'
+    >>> w.render('email', 'test@example.com')
+    u'<input type="text" name="email" value="test@example.com" />'
+    >>> w.render('email', 'some "quoted" & ampersanded value')
+    u'<input type="text" name="email" value="some &quot;quoted&quot; &amp; ampersanded value" />'
+    >>> w.render('email', 'test@example.com', attrs={'class': 'fun'})
+    u'<input type="text" name="email" value="test@example.com" class="fun" />'
+
+    You can also pass 'attrs' to the constructor:
+    >>> w = TextInput(attrs={'class': 'fun'})
+    >>> w.render('email', '')
+    u'<input type="text" class="fun" name="email" />'
+    >>> w.render('email', 'foo@example.com')
+    u'<input type="text" class="fun" value="foo@example.com" name="email" />'
+
+    'attrs' passed to render() get precedence over those passed to the constructor:
+    >>> w = TextInput(attrs={'class': 'pretty'})
+    >>> w.render('email', '', attrs={'class': 'special'})
+    u'<input type="text" class="special" name="email" />'
+    """
+    def render(self, name, value, attrs=None):
+        if value in EMPTY_VALUES: value = ''
+        final_attrs = dict(self.attrs, type='text', name=name)
+        if attrs:
+            final_attrs.update(attrs)
+        if value != '': final_attrs['value'] = value # Only add the 'value' attribute if a value is non-empty.
+        return u'<input %s />' % flatatt(final_attrs)
+
+class Textarea(Widget):
+    """
+    >>> w = Textarea()
+    >>> w.render('msg', '')
+    u'<textarea name="msg"></textarea>'
+    >>> w.render('msg', None)
+    u'<textarea name="msg"></textarea>'
+    >>> w.render('msg', 'value')
+    u'<textarea name="msg">value</textarea>'
+    >>> w.render('msg', 'some "quoted" & ampersanded value')
+    u'<textarea name="msg">some &quot;quoted&quot; &amp; ampersanded value</textarea>'
+    >>> w.render('msg', 'value', attrs={'class': 'pretty'})
+    u'<textarea name="msg" class="pretty">value</textarea>'
+
+    You can also pass 'attrs' to the constructor:
+    >>> w = Textarea(attrs={'class': 'pretty'})
+    >>> w.render('msg', '')
+    u'<textarea class="pretty" name="msg"></textarea>'
+    >>> w.render('msg', 'example')
+    u'<textarea class="pretty" name="msg">example</textarea>'
+
+    'attrs' passed to render() get precedence over those passed to the constructor:
+    >>> w = Textarea(attrs={'class': 'pretty'})
+    >>> w.render('msg', '', attrs={'class': 'special'})
+    u'<textarea class="special" name="msg"></textarea>'
+    """
+    def render(self, name, value, attrs=None):
+        if value in EMPTY_VALUES: value = ''
+        final_attrs = dict(self.attrs, name=name)
+        if attrs:
+            final_attrs.update(attrs)
+        return u'<textarea %s>%s</textarea>' % (flatatt(final_attrs), escape(value))
+
+class CheckboxInput(Widget):
+    """
+    >>> w = CheckboxInput()
+    >>> w.render('is_cool', '')
+    u'<input type="checkbox" name="is_cool" />'
+    >>> w.render('is_cool', False)
+    u'<input type="checkbox" name="is_cool" />'
+    >>> w.render('is_cool', True)
+    u'<input checked="checked" type="checkbox" name="is_cool" />'
+    >>> w.render('is_cool', False, attrs={'class': 'pretty'})
+    u'<input type="checkbox" name="is_cool" class="pretty" />'
+
+    You can also pass 'attrs' to the constructor:
+    >>> w = CheckboxInput(attrs={'class': 'pretty'})
+    >>> w.render('is_cool', '')
+    u'<input type="checkbox" class="pretty" name="is_cool" />'
+
+    'attrs' passed to render() get precedence over those passed to the constructor:
+    >>> w = CheckboxInput(attrs={'class': 'pretty'})
+    >>> w.render('is_cool', '', attrs={'class': 'special'})
+    u'<input type="checkbox" class="special" name="is_cool" />'
+    """
+    def render(self, name, value, attrs=None):
+        final_attrs = dict(self.attrs, type='checkbox', name=name)
+        if attrs:
+            final_attrs.update(attrs)
+        if value: final_attrs['checked'] = 'checked'
+        return u'<input %s />' % flatatt(final_attrs)
+
+##########
+# FIELDS #
+##########
+
+# These values, if given to to_python(), will trigger the self.required check.
+EMPTY_VALUES = (None, '')
+
+class Field(object):
+    widget = TextInput # Default widget to use when rendering this type of Field.
+
+    def __init__(self, required=True, widget=None):
+        self.required = required
+        widget = widget or self.widget
+        if isinstance(widget, type):
+            widget = widget()
+        self.widget = widget
+
+    def to_python(self, value):
+        """
+        Validates the given value and returns its "normalized" value as an
+        appropriate Python object.
+
+        Raises ValidationError for any errors.
+        """
+        if self.required and value in EMPTY_VALUES:
+            raise ValidationError(u'This field is required.')
+        return value
+
+class CharField(Field):
+    """
+    >>> f = CharField(required=False)
+    >>> f.to_python(1)
+    u'1'
+    >>> f.to_python('hello')
+    u'hello'
+    >>> f.to_python(None)
+    u''
+    >>> f.to_python([1, 2, 3])
+    u'[1, 2, 3]'
+
+    CharField accepts an optional max_length parameter:
+    >>> f = CharField(max_length=10, required=False)
+    >>> f.to_python('')
+    u''
+    >>> f.to_python('12345')
+    u'12345'
+    >>> f.to_python('1234567890')
+    u'1234567890'
+    >>> f.to_python('1234567890a')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Ensure this value has at most 10 characters.']
+
+    CharField accepts an optional min_length parameter:
+    >>> f = CharField(min_length=10, required=False)
+    >>> f.to_python('')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Ensure this value has at least 10 characters.']
+    >>> f.to_python('12345')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Ensure this value has at least 10 characters.']
+    >>> f.to_python('1234567890')
+    u'1234567890'
+    >>> f.to_python('1234567890a')
+    u'1234567890a'
+    """
+    def __init__(self, max_length=None, min_length=None, required=True, widget=None):
+        Field.__init__(self, required, widget)
+        self.max_length, self.min_length = max_length, min_length
+
+    def to_python(self, value):
+        "Validates max_length and min_length. Returns a Unicode object."
+        Field.to_python(self, value)
+        if value in EMPTY_VALUES: value = u''
+        if not isinstance(value, basestring):
+            value = unicode(str(value), DEFAULT_ENCODING)
+        elif not isinstance(value, unicode):
+            value = unicode(value, DEFAULT_ENCODING)
+        if self.max_length is not None and len(value) > self.max_length:
+            raise ValidationError(u'Ensure this value has at most %d characters.' % self.max_length)
+        if self.min_length is not None and len(value) < self.min_length:
+            raise ValidationError(u'Ensure this value has at least %d characters.' % self.min_length)
+        return value
+
+class IntegerField(Field):
+    """
+    >>> f = IntegerField()
+    >>> f.to_python('1')
+    1
+    >>> isinstance(f.to_python('1'), int)
+    True
+    >>> f.to_python('23')
+    23
+    >>> f.to_python('a')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a whole number.']
+    >>> f.to_python('1 ')
+    1
+    >>> f.to_python(' 1')
+    1
+    >>> f.to_python(' 1 ')
+    1
+    >>> f.to_python('1a')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a whole number.']
+    """
+    def to_python(self, value):
+        """
+        Validates that int() can be called on the input. Returns the result
+        of int().
+        """
+        super(IntegerField, self).to_python(value)
+        try:
+            return int(value)
+        except (ValueError, TypeError):
+            raise ValidationError(u'Enter a whole number.')
+
+DEFAULT_DATE_INPUT_FORMATS = (
+    '%Y-%m-%d', '%m/%d/%Y', '%m/%d/%y', # '2006-10-25', '10/25/2006', '10/25/06'
+    '%b %d %Y', '%b %d, %Y',            # 'Oct 25 2006', 'Oct 25, 2006'
+    '%d %b %Y', '%d %b, %Y',            # '25 Oct 2006', '25 Oct, 2006'
+    '%B %d %Y', '%B %d, %Y',            # 'October 25 2006', 'October 25, 2006'
+    '%d %B %Y', '%d %B, %Y',            # '25 October 2006', '25 October, 2006'
+)
+
+class DateField(Field):
+    """
+    >>> import datetime
+    >>> f = DateField()
+    >>> f.to_python(datetime.date(2006, 10, 25))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59, 200))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('2006-10-25')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('10/25/2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('10/25/06')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('Oct 25 2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('October 25 2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('October 25, 2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('25 October 2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('25 October, 2006')
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('2006-4-31')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    >>> f.to_python('200a-10-25')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    >>> f.to_python('25/10/06')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    >>> f.to_python(None)
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'This field is required.']
+
+    >>> f = DateField(required=False)
+    >>> f.to_python(None)
+    >>> repr(f.to_python(None))
+    'None'
+    >>> f.to_python('')
+    >>> repr(f.to_python(''))
+    'None'
+
+    DateField accepts an optional input_formats parameter:
+    >>> f = DateField(input_formats=['%Y %m %d'])
+    >>> f.to_python(datetime.date(2006, 10, 25))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30))
+    datetime.date(2006, 10, 25)
+    >>> f.to_python('2006 10 25')
+    datetime.date(2006, 10, 25)
+
+    The input_formats parameter overrides all default input formats,
+    so the default formats won't work unless you specify them:
+    >>> f.to_python('2006-10-25')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    >>> f.to_python('10/25/2006')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    >>> f.to_python('10/25/06')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date.']
+    """
+    def __init__(self, input_formats=None, required=True, widget=None):
+        Field.__init__(self, required, widget)
+        self.input_formats = input_formats or DEFAULT_DATE_INPUT_FORMATS
+
+    def to_python(self, value):
+        """
+        Validates that the input can be converted to a date. Returns a Python
+        datetime.date object.
+        """
+        Field.to_python(self, value)
+        if value in EMPTY_VALUES:
+            return None
+        if isinstance(value, datetime.datetime):
+            return value.date()
+        if isinstance(value, datetime.date):
+            return value
+        for format in self.input_formats:
+            try:
+                return datetime.date(*time.strptime(value, format)[:3])
+            except ValueError:
+                continue
+        raise ValidationError(u'Enter a valid date.')
+
+DEFAULT_DATETIME_INPUT_FORMATS = (
+    '%Y-%m-%d %H:%M:%S',     # '2006-10-25 14:30:59'
+    '%Y-%m-%d %H:%M',        # '2006-10-25 14:30'
+    '%Y-%m-%d',              # '2006-10-25'
+    '%m/%d/%Y %H:%M:%S',     # '10/25/2006 14:30:59'
+    '%m/%d/%Y %H:%M',        # '10/25/2006 14:30'
+    '%m/%d/%Y',              # '10/25/2006'
+    '%m/%d/%y %H:%M:%S',     # '10/25/06 14:30:59'
+    '%m/%d/%y %H:%M',        # '10/25/06 14:30'
+    '%m/%d/%y',              # '10/25/06'
+)
+
+class DateTimeField(Field):
+    """
+    >>> import datetime
+    >>> f = DateTimeField()
+    >>> f.to_python(datetime.date(2006, 10, 25))
+    datetime.datetime(2006, 10, 25, 0, 0)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30))
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59))
+    datetime.datetime(2006, 10, 25, 14, 30, 59)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59, 200))
+    datetime.datetime(2006, 10, 25, 14, 30, 59, 200)
+    >>> f.to_python('2006-10-25 14:30:45')
+    datetime.datetime(2006, 10, 25, 14, 30, 45)
+    >>> f.to_python('2006-10-25 14:30:00')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('2006-10-25 14:30')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('2006-10-25')
+    datetime.datetime(2006, 10, 25, 0, 0)
+    >>> f.to_python('10/25/2006 14:30:45')
+    datetime.datetime(2006, 10, 25, 14, 30, 45)
+    >>> f.to_python('10/25/2006 14:30:00')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('10/25/2006 14:30')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('10/25/2006')
+    datetime.datetime(2006, 10, 25, 0, 0)
+    >>> f.to_python('10/25/06 14:30:45')
+    datetime.datetime(2006, 10, 25, 14, 30, 45)
+    >>> f.to_python('10/25/06 14:30:00')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('10/25/06 14:30')
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python('10/25/06')
+    datetime.datetime(2006, 10, 25, 0, 0)
+    >>> f.to_python('hello')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date/time.']
+    >>> f.to_python('2006-10-25 4:30 p.m.')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date/time.']
+
+    DateField accepts an optional input_formats parameter:
+    >>> f = DateTimeField(input_formats=['%Y %m %d %I:%M %p'])
+    >>> f.to_python(datetime.date(2006, 10, 25))
+    datetime.datetime(2006, 10, 25, 0, 0)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30))
+    datetime.datetime(2006, 10, 25, 14, 30)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59))
+    datetime.datetime(2006, 10, 25, 14, 30, 59)
+    >>> f.to_python(datetime.datetime(2006, 10, 25, 14, 30, 59, 200))
+    datetime.datetime(2006, 10, 25, 14, 30, 59, 200)
+    >>> f.to_python('2006 10 25 2:30 PM')
+    datetime.datetime(2006, 10, 25, 14, 30)
+
+    The input_formats parameter overrides all default input formats,
+    so the default formats won't work unless you specify them:
+    >>> f.to_python('2006-10-25 14:30:45')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid date/time.']
+    """
+    def __init__(self, input_formats=None, required=True, widget=None):
+        Field.__init__(self, required, widget)
+        self.input_formats = input_formats or DEFAULT_DATETIME_INPUT_FORMATS
+
+    def to_python(self, value):
+        """
+        Validates that the input can be converted to a datetime. Returns a
+        Python datetime.datetime object.
+        """
+        Field.to_python(self, value)
+        if value in EMPTY_VALUES:
+            return None
+        if isinstance(value, datetime.datetime):
+            return value
+        if isinstance(value, datetime.date):
+            return datetime.datetime(value.year, value.month, value.day)
+        for format in self.input_formats:
+            try:
+                return datetime.datetime(*time.strptime(value, format)[:6])
+            except ValueError:
+                continue
+        raise ValidationError(u'Enter a valid date/time.')
+
+class RegexField(Field):
+    """
+    >>> import re
+
+    >>> f = RegexField('^\d[A-F]\d$')
+    >>> f.to_python('2A2')
+    u'2A2'
+    >>> f.to_python('3F3')
+    u'3F3'
+    >>> f.to_python('3G3')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+    >>> f.to_python(' 2A2')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+    >>> f.to_python('2A2 ')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+
+    Alternatively, RegexField can take a compiled regular expression:
+    >>> f = RegexField(re.compile('^\d[A-F]\d$'))
+    >>> f.to_python('2A2')
+    u'2A2'
+    >>> f.to_python('3F3')
+    u'3F3'
+    >>> f.to_python('3G3')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+    >>> f.to_python(' 2A2')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+    >>> f.to_python('2A2 ')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid value.']
+
+    RegexField takes an optional error_message argument:
+    >>> f = RegexField('^\d\d\d\d$', 'Enter a four-digit number.')
+    >>> f.to_python('1234')
+    u'1234'
+    >>> f.to_python('123')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a four-digit number.']
+    >>> f.to_python('abcd')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a four-digit number.']
+    """
+    def __init__(self, regex, error_message=None, required=True, widget=None):
+        """
+        regex can be either a string or a compiled regular expression object.
+        error_message is an optional error message to use, if
+        'Enter a valid value' is too generic for you.
+        """
+        Field.__init__(self, required, widget)
+        if isinstance(regex, basestring):
+            regex = re.compile(regex)
+        self.regex = regex
+        self.error_message = error_message or u'Enter a valid value.'
+
+    def to_python(self, value):
+        """
+        Validates that the input matches the regular expression. Returns a
+        Unicode object.
+        """
+        Field.to_python(self, value)
+        if value in EMPTY_VALUES: value = u''
+        if not isinstance(value, basestring):
+            value = unicode(str(value), DEFAULT_ENCODING)
+        elif not isinstance(value, unicode):
+            value = unicode(value, DEFAULT_ENCODING)
+        if not self.regex.search(value):
+            raise ValidationError(self.error_message)
+        return value
+
+email_re = re.compile(
+    r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*"  # dot-atom
+    r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-011\013\014\016-\177])*"' # quoted-string
+    r')@(?:[A-Z0-9-]+\.)+[A-Z]{2,6}$', re.IGNORECASE)  # domain
+
+class EmailField(RegexField):
+    """
+    >>> f = EmailField()
+    >>> f.to_python('person@example.com')
+    u'person@example.com'
+    >>> f.to_python('foo')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid e-mail address.']
+    >>> f.to_python('foo@')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid e-mail address.']
+    >>> f.to_python('foo@bar')
+    Traceback (most recent call last):
+    ...
+    ValidationError: [u'Enter a valid e-mail address.']
+    """
+    def __init__(self, required=True, widget=None):
+        RegexField.__init__(self, email_re, u'Enter a valid e-mail address.', required, widget)
+
+class BooleanField(Field):
+    """
+    >>> f = BooleanField()
+    >>> f.to_python(True)
+    True
+    >>> f.to_python(False)
+    False
+    >>> f.to_python(1)
+    True
+    >>> f.to_python(0)
+    False
+    >>> f.to_python('Django rocks')
+    True
+    """
+    widget = CheckboxInput
+
+    def to_python(self, value):
+        "Returns a Python boolean object."
+        Field.to_python(self, value)
+        return bool(value)
+
+#########
+# FORMS #
+#########
+
+class DeclarativeFieldsMetaclass(type):
+    "Metaclass that converts Field attributes to a dictionary called 'fields'."
+    def __new__(cls, name, bases, attrs):
+        attrs['fields'] = dict([(name, attrs.pop(name)) for name, obj in attrs.items() if isinstance(obj, Field)])
+        return type.__new__(cls, name, bases, attrs)
+
+class Form(object):
+    "A collection of Fields, plus their associated data."
+    __metaclass__ = DeclarativeFieldsMetaclass
+
+    def __init__(self, data=None): # TODO: prefix stuff
+        self.data = data or {}
+        self.__data_python = None # Stores the data after to_python() has been called.
+        self.__errors = None # Stores the errors after to_python() has been called.
+
+    def __iter__(self):
+        for name, field in self.fields.items():
+            yield BoundField(self, field, name)
+
+    def to_python(self):
+        if self.__errors is None:
+            self._validate()
+        return self.__data_python
+
+    def errors(self):
+        "Returns an ErrorDict for self.data"
+        if self.__errors is None:
+            self._validate()
+        return self.__errors
+
+    def is_valid(self):
+        """
+        Returns True if the form has no errors. Otherwise, False. This exists
+        solely for convenience, so client code can use positive logic rather
+        than confusing negative logic ("if not form.errors()").
+        """
+        return not bool(self.errors())
+
+    def __getitem__(self, name):
+        "Returns a BoundField with the given name."
+        try:
+            field = self.fields[name]
+        except KeyError:
+            raise KeyError('Key %r not found in Form' % name)
+        return BoundField(self, field, name)
+
+    def _validate(self):
+        data_python = {}
+        errors = ErrorDict()
+        for name, field in self.fields.items():
+            try:
+                value = field.to_python(self.data.get(name, None))
+                data_python[name] = value
+            except ValidationError, e:
+                errors[name] = e.messages
+        if not errors: # Only set self.data_python if there weren't errors.
+            self.__data_python = data_python
+        self.__errors = errors
+
+class BoundField(object):
+    "A Field plus data"
+    def __init__(self, form, field, name):
+        self._form = form
+        self._field = field
+        self._name = name
+
+    def __str__(self):
+        "Renders this field as an HTML widget."
+        # Use the 'widget' attribute on the field to determine which type
+        # of HTML widget to use.
+        return self.as_widget(self._field.widget)
+
+    def _errors(self):
+        """
+        Returns an ErrorList for this field. Returns an empty ErrorList
+        if there are none.
+        """
+        try:
+            return self._form.errors()[self._name]
+        except KeyError:
+            return ErrorList()
+    errors = property(_errors)
+
+    def as_widget(self, widget, attrs=None):
+        return widget.render(self._name, self._form.data.get(self._name, None), attrs=attrs)
+
+    def as_text(self, attrs=None):
+        """
+        Returns a string of HTML for representing this as an <input type="text">.
+        """
+        return self.as_widget(TextInput(), attrs)
+
+    def as_textarea(self, attrs=None):
+        "Returns a string of HTML for representing this as a <textarea>."
+        return self.as_widget(Textarea(), attrs)
+
+##########################
+# DATABASE API SHORTCUTS #
+##########################
+
+def form_for_model(model):
+    "Returns a Form instance for the given Django model class."
+    raise NotImplementedError
+
+def form_for_fields(field_list):
+    "Returns a Form instance for the given list of Django database field instances."
+    raise NotImplementedError
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()