Deal with NoneType access.

The `NoneType` object is not available from the `types` module in
python 3. This is a workaronud to deal with that.

common/lib/xmodule/xmodule/modulestore/mongoengine_fields.py

@@ -1,11 +1,12 @@
 """
 Custom field types for mongoengine
 """
+from __future__ import absolute_import
 import mongoengine
 from opaque_keys.edx.locations import Location
-from types import NoneType
 from opaque_keys.edx.keys import CourseKey, UsageKey
 from six import text_type
+import six
 
 
 class CourseKeyField(mongoengine.StringField):
@@ -20,7 +21,7 @@ class CourseKeyField(mongoengine.StringField):
         """
         For now saves the course key in the deprecated form
         """
-        assert isinstance(course_key, (NoneType, CourseKey))
+        assert isinstance(course_key, (type(None), CourseKey))
         if course_key:
             # don't call super as base.BaseField.to_mongo calls to_python() for some odd reason
             return text_type(course_key)
@@ -33,16 +34,16 @@ class CourseKeyField(mongoengine.StringField):
         """
         # calling super b/c it decodes utf (and doesn't have circularity of from_python)
         course_key = super(CourseKeyField, self).to_python(course_key)
-        assert isinstance(course_key, (NoneType, basestring, CourseKey))
+        assert isinstance(course_key, (type(None), six.string_types, CourseKey))
         if course_key == '':
             return None
-        if isinstance(course_key, basestring):
+        if isinstance(course_key, six.string_types):
             return CourseKey.from_string(course_key)
         else:
             return course_key
 
     def validate(self, value):
-        assert isinstance(value, (NoneType, basestring, CourseKey))
+        assert isinstance(value, (type(None), six.string_types, CourseKey))
         if isinstance(value, CourseKey):
             return super(CourseKeyField, self).validate(text_type(value))
         else:
@@ -60,7 +61,7 @@ class UsageKeyField(mongoengine.StringField):
         """
         For now saves the usage key in the deprecated location i4x/c4x form
         """
-        assert isinstance(location, (NoneType, UsageKey))
+        assert isinstance(location, (type(None), UsageKey))
         if location is None:
             return None
         return super(UsageKeyField, self).to_mongo(text_type(location))
@@ -69,17 +70,17 @@ class UsageKeyField(mongoengine.StringField):
         """
         Deserialize to a UsageKey instance: for now it's a location missing the run
         """
-        assert isinstance(location, (NoneType, basestring, UsageKey))
+        assert isinstance(location, (type(None), six.string_types, UsageKey))
         if location == '':
             return None
-        if isinstance(location, basestring):
+        if isinstance(location, six.string_types):
             location = super(UsageKeyField, self).to_python(location)
             return Location.from_string(location)
         else:
             return location
 
     def validate(self, value):
-        assert isinstance(value, (NoneType, basestring, UsageKey))
+        assert isinstance(value, (type(None), six.string_types, UsageKey))
         if isinstance(value, UsageKey):
             return super(UsageKeyField, self).validate(text_type(value))
         else:

lms/djangoapps/discussion/django_comment_client/permissions.py

@@ -6,7 +6,6 @@ Module for checking permissions with the comment_client backend
 from __future__ import absolute_import
 
 import logging
-from types import NoneType
 
 import six
 from edx_django_utils.cache import DEFAULT_REQUEST_CACHE
@@ -23,7 +22,7 @@ from openedx.core.lib.cache_utils import request_cached
 
 
 def has_permission(user, permission, course_id=None):
-    assert isinstance(course_id, (NoneType, CourseKey))
+    assert isinstance(course_id, (type(None), CourseKey))
     request_cache_dict = DEFAULT_REQUEST_CACHE.data
     cache_key = "django_comment_client.permissions.has_permission.all_permissions.{}.{}".format(
         user.id, course_id