Refactor Instructor Tasks - in prep for Grade report work

lms/djangoapps/instructor_task/subtasks.py

@@ -14,9 +14,12 @@ import dogstats_wrapper as dog_stats_api
 from django.db import transaction, DatabaseError
 from django.core.cache import cache
 
-from lms.djangoapps.instructor_task.models import InstructorTask, PROGRESS, QUEUING
 from util.db import outer_atomic
 
+from .exceptions import DuplicateTaskException
+from .models import InstructorTask, PROGRESS, QUEUING
+
+
 TASK_LOG = logging.getLogger('edx.celery.task')
 
 # Lock expiration should be long enough to allow a subtask to complete.
@@ -26,11 +29,6 @@ SUBTASK_LOCK_EXPIRE = 60 * 10  # Lock expires in 10 minutes
 MAX_DATABASE_LOCK_RETRIES = 5
 
 
-class DuplicateTaskException(Exception):
-    """Exception indicating that a task already exists or has already completed."""
-    pass
-
-
 def _get_number_of_subtasks(total_num_items, items_per_task):
     """
     Determines number of subtasks that would be generated by _generate_items_for_subtask.