code: def create_stream_subscription(self, stream, on_data, timeout=60):
          
          options = rest_pb2.StreamSubscribeRequest()
          options.stream = stream
  
          manager = WebSocketSubscriptionManager(
              self._client, resource='stream', options=options)
  
          # Represent subscription as a future
          subscription = WebSocketSubscriptionFuture(manager)
  
          wrapped_callback = functools.partial(
              _wrap_callback_parse_stream_data, subscription, on_data)
  
          manager.open(wrapped_callback, instance=self._instance)
  
          # Wait until a reply or exception is received
          subscription.reply(timeout=timeout)
  
          return subscription
docs: Create a new stream subscription.
  
          :param str stream: The name of the stream.
          :param on_data: Function that gets called with  :class:`.StreamData`
                          updates.
          :param float timeout: The amount of seconds to wait for the request
                                to complete.
          :return: Future that can be used to manage the background websocket
                   subscription
          :rtype: .WebSocketSubscriptionFuture