code: def was_persisted(self):
          
          pk_name = self._meta.pk.name
          return bool(self.old_state()[pk_name])
docs: Returns true if the instance was persisted (saved) in its old
          state.
  
          Examples::
  
              >>> user = User()
              >>> user.save()
              >>> user.was_persisted()
              False
  
              >>> user = User.objects.get(pk=1)
              >>> user.delete()
              >>> user.was_persisted()
              True