'Get or create cache directory for the extension.
Use this directory to cache data that can safely be thrown away.
:param config: the Mopidy config object
:return: string'

@classmethod
def get_cache_dir(cls, config):

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