code: def listen_to_node(self, id_):
          
          if r_client.get(id_) is None:
              return
          else:
              self.toredis.subscribe(_pubsub_key(id_), callback=self.callback)
              self._listening_to[_pubsub_key(id_)] = id_
              return id_
docs: Attach a callback on the job pubsub if it exists