INCR-437 python3 compatibility

lms/djangoapps/grades/migrations/0005_multiple_course_flags.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-from __future__ import unicode_literals
+from __future__ import absolute_import, unicode_literals
 
 from django.db import migrations, models
 from opaque_keys.edx.django.models import CourseKeyField

lms/djangoapps/grades/migrations/0006_persistent_course_grades.py

@@ -1,10 +1,11 @@
 # -*- coding: utf-8 -*-
-from __future__ import unicode_literals
+from __future__ import absolute_import, unicode_literals
 
-from django.db import migrations, models
 import django.utils.timezone
 import model_utils.fields
+from django.db import migrations, models
 from opaque_keys.edx.django.models import CourseKeyField
+
 import coursewarehistoryextended.fields
 
 

lms/djangoapps/grades/migrations/0013_persistentsubsectiongradeoverride.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-from __future__ import unicode_literals
+from __future__ import absolute_import, unicode_literals
 
 from django.db import migrations, models
 

lms/djangoapps/grades/rest_api/serializers.py

@@ -1,6 +1,8 @@
 """
 API Serializers
 """
+from __future__ import absolute_import
+
 from collections import defaultdict
 
 from rest_framework import serializers

lms/djangoapps/grades/rest_api/urls.py

@@ -2,8 +2,9 @@
 Grades API URLs.
 """
 
-from django.conf.urls import include, url
+from __future__ import absolute_import
 
+from django.conf.urls import include, url
 
 app_name = 'lms.djangoapps.grades'