纳斯达克仅支持字符串'symbols'

Question

import pandas_datareader as web
import datetime

start = datetime.datetime(2015, 1, 1)
end = datetime.datetime(2018, 7, 30)

f = web.DataReader("AAPL", "nasdaq", start, end)

我运行这段代码，结果是这样的

File "/anaconda3/lib/python3.6/site-packages/pandas_datareader/data.py", line 377, in DataReader
    "Nasdaq, not %r" % (name,))
ValueError: Only the string 'symbols' is supported for Nasdaq, not 'AAPL'

所以我该如何解决这个问题。