Fixed code duplication in task listing api on instructor dashboard

lms/djangoapps/instructor_task/tasks_helper/module_state.py

@@ -5,7 +5,6 @@ import json
 import logging
 from time import time
 
-from django.contrib.auth.models import User
 from django.utils.translation import ugettext_noop
 from opaque_keys.edx.keys import UsageKey
 
@@ -16,6 +15,7 @@ from courseware.model_data import DjangoKeyValueStore, FieldDataCache
 from courseware.models import StudentModule
 from courseware.module_render import get_module_for_descriptor_internal
 from lms.djangoapps.grades.events import GRADES_OVERRIDE_EVENT_TYPE, GRADES_RESCORE_EVENT_TYPE
+from student.models import get_user_by_username_or_email
 from track.event_transaction_utils import create_new_event_transaction_id, set_event_transaction_type
 from track.views import task_track
 from util.db import outer_atomic
@@ -409,12 +409,7 @@ def _get_modules_to_update(course_id, usage_keys, student_identifier, filter_fcn
     """
     def get_student():
         """ Fetches student instance if an identifier is provided, else return None """
-        if student_identifier is None:
-            return None
-
-        student_identifier_type = 'email' if '@' in student_identifier else 'username'
-        student_query_params = {student_identifier_type: student_identifier}
-        return User.objects.get(**student_query_params)
+        return None if not student_identifier else get_user_by_username_or_email(student_identifier)
 
     module_query_params = {'course_id': course_id, 'module_state_keys': usage_keys}