去年我一直使用此代码从雅虎财经提取（抓取）股票价格，但现在它产生了错误。有谁知道为什么会发生这种情况以及如何解决它？
# Importing necessary packages
from pandas_datareader import data as web
import datetime as dt
import matplotlib.pyplot as plt
import pandas as pd
import os
import numpy as np
# Stock selection from Yahoo Finance
stock = input("Enter stock symbol or ticket symbol (Exp. General Electric is 'GE'): ")
# Visualizing the stock over time and setting up the dataframe
start_date = (dt.datetime.now() - dt.timedelta(days=40000)).strftime("%m-%d-%Y")
df = web.DataReader(stock, data_source='yahoo', start=start_date)
#THE ERROR IS ON THIS LINE^
plt.plot(df['Close'])
plt.title('Stock Prices Over …