code: def notify_listeners(self, data: Optional[_ListenableDataType]=_NO_DATA_MARKER):
          
          for listener in self._listeners:
              if data is not Listenable._NO_DATA_MARKER:
                  listener(data)
              else:
                  listener()
docs: Notify event listeners, passing them the given data (if any).
          :param data: the data to pass to the event listeners