Python中利用quantOS中的jaqs访问数据,返回None为什么呀

已经下载好相关的包了

from jaqs.data.dataapi import DataApi

api=DataApi(addr="tcp://data.quantos.org:8910")
token='eyJhbGciOiJIUzI1NiJ9.eyJjcmVhdGVfdGltZSI6IjE1NzY4OTE4OTEyMDgiLCJpc3MiOiJhdXRoMCIsImlkIjoiMTczMjAwNjM1NjkifQ.-62zIY--kIccxcyv8JkI4gyYwHeTuxzL-opEArRKY24'
api.login('17320063569',token)

df, msg = api.daily(
symbol="600832.SH, 600030.SH",
start_date=20121026,
end_date=20121130,
fields="",
adjust_mode="post")

您好请问为什么返回的结果是None呀