docs: def add_hook_pull(self, address, callback):
          """Same as above, but with a PULL socket.
          (e.g good for pushed 'inproc' messages from another thread).
          """
          LOGGER.info("Subscriber adding PULL hook %s", str(address))
          socket = get_context().socket(PULL)
          socket.connect(address)
          self._add_hook(socket, callback)