docs: def _create_listening_stream(self, pull_addr):
          """
          Create a stream listening for Requests. The `self._recv_callback`
          method is asociated with incoming requests.
          """
          sock = self._zmq_context.socket(zmq.PULL)
          sock.connect(pull_addr)
          stream = ZMQStream(sock, io_loop=self.io_loop)
  
          return stream