Stock API and plot function update

[TianYuanSX]

Hi Jingles,

Thanks for this great tutorial. I'm a student interested in Python finance.

I found some parts of the code require updates. And I tried to fix them.

• plt.grid() no longer accepts keyword b=None. I just removed it. otherwise, this function will raise an exception. See matplotlib.pyplot.grid
• Fetching the daily adjusted close price is a premium feature now, while a Free API cannot retrieve such data. The daily close price was used instead. See Alpha Vantage API Documentation

Best regards, Yuan