增加一行
hangzhou = zhewan_score_original[zhewan_score_original.城市 == '杭州市']
hangzhou_d = hangzhou.服务分.describe()
hangzhou_d.loc['90分以下'] = len(
hangzhou[hangzhou.服务分<90])
hangzhou_d.loc['80分以下'] = len(
hangzhou[hangzhou.服务分<80])
hangzhou_d.loc['70分以下'] = len(
hangzhou[hangzhou.服务分<70])