def get_class(class_key):
    """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
    """
    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]
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