code: def reply(self, timeout=None):
          
          self._wait_on_signal(self._response_received)
          if self._response_exception is not None:
              msg = self._response_exception.message
              raise YamcsError(msg)
          return self._response_reply
docs: Returns the initial reply. This is emitted before any subscription
          data is emitted. This function raises an exception if the subscription
          attempt failed.