code: def _handle_subscribed(self, *args,  chanId=None, channel=None, **kwargs):
          
          log.debug("_handle_subscribed: %s - %s - %s", chanId, channel, kwargs)
          if chanId in self.channels:
              raise AlreadyRegisteredError()
  
          self._heartbeats[chanId] = time.time()
  
          try:
              channel_key = ('raw_'+channel
                             if kwargs['prec'].startswith('R') and channel == 'book'
                             else channel)
          except KeyError:
              channel_key = channel
  
          try:
              self.channels[chanId] = self._data_handlers[channel_key]
          except KeyError:
              raise UnknownChannelError()
  
          # prep kwargs to be used as secondary value in dict key
          try:
              kwargs.pop('event')
          except KeyError:
              pass
  
          try:
              kwargs.pop('len')
          except KeyError:
              pass
  
          try:
              kwargs.pop('chanId')
          except KeyError:
              pass
  
          self.channel_labels[chanId] = (channel_key, kwargs)
docs: Handles responses to subscribe() commands - registers a channel id with
          the client and assigns a data handler to it.
          :param chanId: int, represent channel id as assigned by server
          :param channel: str, represents channel name