INCR-288 Run python-modernize on lms/djangoapps/coursewarehistoryextended (#20595)

* run python modernize

* run isort

lms/djangoapps/coursewarehistoryextended/fields.py

@@ -2,6 +2,8 @@
 Custom fields for use in the coursewarehistoryextended django app.
 """
 
+from __future__ import absolute_import
+
 from django.db.models.fields import AutoField
 from django.db.models.fields.related import OneToOneField
 

lms/djangoapps/coursewarehistoryextended/migrations/0001_initial.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from __future__ import absolute_import
 from django.db import migrations, models
 import django.db.models.deletion
 import coursewarehistoryextended.fields

lms/djangoapps/coursewarehistoryextended/migrations/0002_force_studentmodule_index.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from __future__ import absolute_import
 from django.db import migrations, models
 
 

lms/djangoapps/coursewarehistoryextended/models.py

@@ -12,6 +12,9 @@ file and check it in at the same time as your model changes. To do that,
 ASSUMPTIONS: modules have unique IDs, even across different module_types
 
 """
+from __future__ import absolute_import
+
+import six
 from django.db import models
 from django.db.models.signals import post_delete, post_save
 from django.dispatch import receiver
@@ -62,4 +65,4 @@ class StudentModuleHistoryExtended(BaseStudentModuleHistory):
         StudentModuleHistoryExtended.objects.filter(student_module=instance).all().delete()
 
     def __unicode__(self):
-        return unicode(repr(self))
+        return six.text_type(repr(self))

lms/djangoapps/coursewarehistoryextended/tests.py

@@ -5,6 +5,8 @@ but these are specific to the new storage model with multiple
 backend tables.
 """
 
+from __future__ import absolute_import
+
 import json
 from unittest import skipUnless