:param str op: `add` or `del`

def update_favorite_song(self, song_id, op):
        """
        :param str op: `add` or `del`
        """
        op = 'un' if op == 'del' else ''
        action = 'mtop.alimusic.fav.songfavoriteservice.{}favoritesong'.format(op)
        payload = {
            'songId': song_id
        }
        code, msg, rv = self.request(action, payload)
        return rv['data']['data']['status'] == 'true'