code: def set_volume(self, volume):
          
          volume = min(max(0, volume), 1)
          self.logger.info("Receiver:setting volume to %.1f", volume)
          self.send_message({MESSAGE_TYPE: 'SET_VOLUME',
                             'volume': {'level': volume}})
          return volume
docs: Allows to set volume. Should be value between 0..1.
          Returns the new volume.