Fix EnumFieldMixin.get_choices for enum34 1.1

On Python 2 with enum34 version 1.1.0 or newer, an enum item with zero
value will evaluate to false.  This makes `get_choices` return incorrect
data for the zero item.  Fix this by doing the checking if a choice is
an enum value with `if isinstance(i, Enum)` rather than with `if i`.

Add a test case that checks the choices are correct.

enumfields/fields.py

@@ -70,7 +70,7 @@ def get_choices(self, include_blank=True, blank_choice=BLANK_CHOICE_DASH):
         # Force enum fields' options to use the `value` of the enumeration
         # member as the `value` of SelectFields and similar.
         return [
-            (i.value if i else i, display)
+            (i.value if isinstance(i, Enum) else i, display)
             for (i, display)
             in super(EnumFieldMixin, self).get_choices(include_blank, blank_choice)
         ]

tests/models.py

@@ -38,3 +38,5 @@ class IntegerEnum(IntEnum):
 
     zero_field = EnumIntegerField(ZeroEnum, null=True, default=None, blank=True)
     int_enum = EnumIntegerField(IntegerEnum, null=True, default=None, blank=True)
+
+    zero2 = EnumIntegerField(ZeroEnum, default=ZeroEnum.ZERO)

tests/test_django_admin.py

@@ -45,7 +45,8 @@ def test_model_admin(superuser_client):
         'color': MyModel.Color.RED.value,
         'taste': MyModel.Taste.UMAMI.value,
         'taste_int': MyModel.Taste.SWEET.value,
-        'random_code': secret_uuid
+        'random_code': secret_uuid,
+        'zero2': MyModel.ZeroEnum.ZERO.value,
     }
     response = superuser_client.post(url, follow=True, data=post_data)
     response.render()

tests/test_form_fields.py

@@ -8,7 +8,7 @@
 
 def get_form(**kwargs):
     instance = MyModel(color=MyModel.Color.RED)
-    FormClass = modelform_factory(MyModel, fields=("color",))
+    FormClass = modelform_factory(MyModel, fields=("color", "zero2"))
     return FormClass(instance=instance, **kwargs)
 
 
@@ -22,3 +22,8 @@ def test_unbound_form_with_instance():
 def test_bound_form_with_instance():
     form = get_form(data={"color": "g"})
     assert 'value="g" selected="selected"' in six.text_type(form["color"])
+
+
+def test_choices():
+    form = get_form()
+    assert form.base_fields["zero2"].choices == [(0, 'ZERO'), (1, 'ONE')]