[pandas] index already in datetime (#251)

Author: mmcky

lectures/pandas.md

@@ -695,9 +695,6 @@ def read_data(ticker_list,
     for tick in ticker_list:
         stock = yf.Ticker(tick)
         prices = stock.history(start=start, end=end)
-
-        # Change the index to date
-        prices.index = pd.to_datetime(prices.index.date)
         
         closing_prices = prices['Close']
         ticker[tick] = closing_prices