code: def disconnect(self, cback, subscribers=None, instance=None):
          
          if subscribers is None:
              subscribers = self.subscribers
          # wrapper
          if self._fdisconnect is not None:
              def _disconnect(cback):
                  self._disconnect(subscribers, cback)
  
              notify = partial(self._notify_one, instance)
              if instance is not None:
                  result = self._fdisconnect(instance, cback, subscribers,
                                             _disconnect, notify)
              else:
                  result = self._fdisconnect(cback, subscribers, _disconnect,
                                             notify)
              if inspect.isawaitable(result):
                  result = pull_result(result)
          else:
              self._disconnect(subscribers, cback)
              result = None
          return result
docs: Remove a previously added function or method from the set of the
          signal's handlers.
  
          :param cback: the callback (or *handler*) to be added to the set
          :returns: ``None`` or the value returned by the corresponding wrapper