docs: 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'