'Get or create data directory for the extension.
Use this directory to store data that should be persistent.
:param config: the Mopidy config object
:returns: string'

@classmethod
def get_data_dir(cls, config):

    assert (cls.ext_name is not None)
    data_dir_path = bytes(os.path.join(config[u'core'][u'data_dir'], cls.ext_name))
    path.get_or_create_dir(data_dir_path)
    return data_dir_path
