code: def set_volume(self, volume):
          
          for data in self._group.get('clients'):
              client = self._server.client(data.get('id'))
              yield from client.set_volume(volume, update_group=False)
              client.update_volume({
                  'volume': {
                      'percent': volume,
                      'muted': client.muted
                  }
              })
          _LOGGER.info('set volume to %s on clients in %s', volume, self.friendly_name)
docs: Set volume.