DataDownloader的symbol_list传入一个列表后无法正常监控下载状态

td = DataDownloader(api, symbol_list=quotes, dur_sec=24*60*60,
                    start_dt=startdt, end_dt=date(2018, 1, 1), csv_file_name="index_daily.csv")
 with closing(api):
    while not all([v.is_finished() for v in td.values()]):
        api.wait_update()
        print("progress: ", { k:("%.2f%%" % v.get_progress()) for k,v in td.items() })

当第一个合约数据下载完，代码就退出了