Fixed #20094 - Be more careful when checking for Iterator

Python 2.6 has some different behaviour when checking
isinstance(foo, collections.Iterator).

3 files changed, 18 insertions, 5 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index c210cfabf6..1f0ce5e4ed 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -1,6 +1,5 @@
 from __future__ import unicode_literals
 
-import collections
 import copy
 import datetime
 import decimal
@@ -18,6 +17,7 @@ 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 _
@@ -488,7 +488,7 @@ class Field(object):
         return bound_field_class(self, fieldmapping, original)
 
     def _get_choices(self):
-        if isinstance(self._choices, collections.Iterator):
+        if is_iterator(self._choices):
             choices, self._choices = tee(self._choices)
             return choices
         else:
diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index 754e33292d..42682c342e 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -4,7 +4,6 @@ Code to manage the creation and SQL rendering of 'where' constraints.
 
 from __future__ import absolute_import
 
-import collections
 import datetime
 from itertools import repeat
 
@@ -12,6 +11,7 @@ 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
@@ -58,7 +58,7 @@ class WhereNode(tree.Node):
         if not isinstance(data, (list, tuple)):
             return data
         obj, lookup_type, value = data
-        if isinstance(value, collections.Iterator):
+        if is_iterator(value):
             # Consume any generators immediately, so that we can determine
             # emptiness and transform any non-empty values correctly.
             value = list(value)
diff --git a/django/utils/itercompat.py b/django/utils/itercompat.py
index e7ea326536..c50dcfb779 100644
--- a/django/utils/itercompat.py
+++ b/django/utils/itercompat.py
@@ -4,10 +4,12 @@ Where possible, we try to use the system-native version and only fall back to
 these implementations if necessary.
 """
 
-from django.utils.six.moves import builtins
+import collections
 import itertools
+import sys
 import warnings
 
+
 def is_iterable(x):
     "A implementation independent way of checking for iterables"
     try:
@@ -17,6 +19,17 @@ def is_iterable(x):
     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__')
+
 def product(*args, **kwds):
     warnings.warn("django.utils.itercompat.product is deprecated; use the native version instead",
                   DeprecationWarning, stacklevel=2)