Replaced 'next' testing by collections.Iterator testing.

The new construct is also Python 3 compatible (where 'next' has
been renamed to '__next__').

django/db/models/fields/__init__.py

@@ -1,3 +1,4 @@
+import collections
 import copy
 import datetime
 import decimal
@@ -436,7 +437,7 @@ class Field(object):
         return bound_field_class(self, fieldmapping, original)
 
     def _get_choices(self):
-        if hasattr(self._choices, 'next'):
+        if isinstance(self._choices, collections.Iterator):
             choices, self._choices = tee(self._choices)
             return choices
         else:

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
 
@@ -49,7 +50,7 @@ class WhereNode(tree.Node):
             return
 
         obj, lookup_type, value = data
-        if hasattr(value, '__iter__') and hasattr(value, 'next'):
+        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)