code: def values_list(self, *args, **kwargs):
          
          flat = kwargs.pop('flat', False)
          assert flat is True
          assert len(args) == 1
          assert args[0] == self.model._meta.pk.name
          return self.pks
docs: Return the primary keys as a list.
  
          The only valid call is values_list('pk', flat=True)