pandas使用[]单中括号和[[]]双中括号的区别

close_px = pd.read_csv(u'https://gitee.com/pan19/data-source/raw/master/stock_px_2.csv', parse_dates=True,
                       index_col=0)
close_px.info()
close_px.head(10)

type(close_px[‘SPX’]) 返回 pandas.core.series.Series type(close_px[[‘SPX’]]) 返回 pandas.core.frame.DataFrame