code: def volume_down(self, delta=0.1):
          
          if delta <= 0:
              raise ValueError(
                  "volume delta must be greater than zero, not {}".format(delta))
          return self.set_volume(self.status.volume_level - delta)
docs: Decrement the volume by 0.1 (or delta) unless it is already 0.
          Returns the new volume.