code: def add(self, delta, data):
      
      if delta < 0:
        raise ValueError("Delta time should be always positive")
      self._not_playing.append((delta, iter(data)))
docs: Adds (enqueues) an iterable event to the mixer.
  
      Parameters
      ----------
      delta :
        Time in samples since last added event. This can be zero and can be
        float. Use "s" object from sHz for time conversion.
      data :
        Iterable (e.g. a list, a tuple, a Stream) to be "played" by the mixer at
        the given time delta.
  
      See Also
      --------
      sHz :
        Time in seconds (s) and frequency in hertz (Hz) constants from sample
        rate in samples/second.