old_contents: from django.db.models import Manager
         
  class ShipmentManager(Manager):
  """Returns Shipments that are not delivered""" 
         
      def undelivered(self):
          return self.get_query_set().exclude(status__exact='delivered')
  
new_contents: from django.db.models import Manager
         
  class ShipmentManager(Manager):
  """Returns Shipments that are not delivered""" 
         
      def undelivered(self):
          return self.get_query_set().exclude(status='delivered')
  
subject: Change filter syntax to be more direct.