code: def _propagate_down(self, handle, target_id):
          
          for stream in self.router.get_streams():
              if target_id in stream.egress_ids and (
                      (self.parent is None) or
                      (self.parent.context_id != stream.remote_id)
                  ):
                  self._send_one(stream, mitogen.core.DEL_ROUTE, target_id, None)
docs: For DEL_ROUTE, we additionally want to broadcast the message to any
          stream that has ever communicated with the disconnecting ID, so
          core.py's :meth:`mitogen.core.Router._on_del_route` can turn the
          message into a disconnect event.
  
          :param int handle:
              :data:`mitogen.core.ADD_ROUTE` or :data:`mitogen.core.DEL_ROUTE`
          :param int target_id:
              ID of the connecting or disconnecting context.