Stuck on the Getting NASDAQ Symbols module!

Stuck on this module:
https://www.codecademy.com/paths/finance-python/tracks/introduction-to-pandas-for-finance/modules/importing-finance-data/lessons/importing-finance-data-python/exercises/getting-nasdaq-symbols

My code (see below) is exactly the same as that given in the solution, but I kept getting the error " Expected symbols to be a DataFrame containing NASDAQ stock symbols." Why?? HELP PLEASE!!

import codecademylib3_seaborn

from pandas_datareader.nasdaq_trader import get_nasdaq_symbols

symbols = get_nasdaq_symbols()

print(symbols)