code: def _maybe_notify_connected(self, arg):
          
          if self._connected_listeners is None:
              return
          for d in self._connected_listeners:
              # Twisted will turn this into an errback if "arg" is a
              # Failure
              d.callback(arg)
          self._connected_listeners = None
docs: Internal helper.
  
          .callback or .errback on all Deferreds we've returned from
          `when_connected`