Fix detection of iterator attributes

Test for the exact methods required by the iterator protocol.
(https://docs.python.org/2/library/stdtypes.html#iterator-types)

model_mommy/mommy.py

@@ -241,12 +241,14 @@ def _populate(self):
 
 
 def is_iterator(value):
-    try:
-        iter(value)
-        return not isinstance(value, string_types)
-    except TypeError:
+    if not hasattr(value, '__iter__'):
         return False
 
+    if PY3:
+        return hasattr(value, '__next__')
+    else:
+        return hasattr(value, 'next')
+
 
 class Mommy(object):
     attr_mapping = {}

test/generic/fields.py

@@ -5,3 +5,10 @@ class CustomFieldWithGenerator(models.TextField):
 
 class CustomFieldWithoutGenerator(models.TextField):
     pass
+
+class FakeListField(models.TextField):
+    def to_python(self, value):
+        return value.split()
+
+    def get_prep_value(self, value):
+        return super(FakeListField, self).get_prep_value(' '.join(value))

test/generic/models.py

@@ -246,6 +246,10 @@ class BaseModelForNext(models.Model):
     fk = models.ForeignKey(ModelWithNext)
 
 
+class BaseModelForList(models.Model):
+    fk = FakeListField()
+
+
 if VERSION < (1, 4):
     class DummyIPAddressFieldModel(models.Model):
         ipv4_field = models.IPAddressField()  # Deprecated in Django 1.7

test/generic/tests/test_mommy.py

@@ -20,6 +20,7 @@
 from test.generic.models import DummyGenericForeignKeyModel, NonAbstractPerson
 from test.generic.models import DummyEmptyModel
 from test.generic.models import ModelWithNext, BaseModelForNext
+from test.generic.models import BaseModelForList
 
 
 class ModelFinderTest(TestCase):
@@ -443,6 +444,16 @@ def test_creates_instance_for_model_with_next(self):
         self.assertEqual('foo', instance.fk.next())
 
 
+class MommyHandlesModelWithList(TestCase):
+    def test_creates_instance_for_model_with_list(self):
+        instance = mommy.make(
+            BaseModelForList,
+            fk=["foo"]
+        )
+
+        self.assertTrue(instance.id)
+        self.assertEqual(["foo"], instance.fk)
+
 if VERSION < (1, 4):
     from test.generic.forms import DummyIPAddressFieldForm