code: def get_class(class_key):
      
      if class_key not in CLASSES:
          for basecls in (MediaMetadata, MediaCollection):
              if class_key.startswith(basecls.__name__):
                  # So MediaMetadataTrack turns into MSTrack
                  class_name = 'MS' + class_key.replace(basecls.__name__, '')
                  if sys.version_info[0] == 2:
                      class_name = class_name.encode('ascii')
                  CLASSES[class_key] = type(class_name, (basecls,), {})
                  _LOG.info('Class %s created', CLASSES[class_key])
      return CLASSES[class_key]
docs: Form a music service data structure class from the class key
  
      Args:
          class_key (str): A concatenation of the base class (e.g. MediaMetadata)
              and the class name
  
      Returns:
          class: Subclass of MusicServiceItem