code: def unregister(self, *model_list):
          
          for model in model_list:
              if model not in self.registry:
                  raise NotRegistered('The model %s is not registered' %
                                      model.__name__)
              del self.registry[model]
docs: Unregisters the given model(s).
  
          If a model isn't already registered, this will raise NotRegistered.