old_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  from django.db import models
  from django.utils import timezone
  
  
  class PublishableManager(models.Manager):
      def all_published(self):
          return super(PublishableManager, self).get_query_set().filter(
              date_available__lte=timezone.now(), published=True)
  
new_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  from django.db import models
  from django.utils import timezone
  
  from polymorphic import PolymorphicManager
  
  
  class PublishableManager(PolymorphicManager):
      def all_published(self):
          return super(PublishableManager, self).get_query_set().filter(
              date_available__lte=timezone.now(), published=True)
  
subject: Fix issue #318: Change Manager superclass