tbpy只能查一个上期所的产品吗

import tbpytbpy.init()ss=tbpy.get_history_n(symbol=[\'ur309.CZCE\'], frequency=\'2m\', count=10, flag=tbpy.QuoteFlag.RolloverBackWard|tbpy.QuoteFlag.OnlyNight, fields=[\'open\', \'high\', \'time\'], timeout=\'60s\')print(ss)查不出来，换上期所的就可以