此种方法省去的重复性的循环语句，用一个循环代替了所有

Menu = {    "北京":{            "昌平":["沙河","辛庄","南口"],            "朝阳":["太阳宫","孙河","管庄"],            "海淀":["上地","西三旗","西二旗"]          },    "河南":{            "郑州":["二七区","中原区","金水区"],            "洛阳":["西工区","老城区","洛龙区"]            },    "河北":{            "石家庄":["新华区","长安区","正定县"],            "邯郸":["丛台区","复兴区","大名县"]        },    "广东":{            "广州":["南沙区","花都区","番禹区"],            "深圳":["龙岗区","罗湖区","盐田区"],            "东莞":["南城区","东城区","万江区"]    },}cur_menu = Menuparrent_menu = []while True:    for keys in cur_menu:        print(keys)    choice = input("请选择>>>").strip()    if len(choice) == 0:        continue    if choice in cur_menu:        parrent_menu.append(cur_menu)        cur_menu = cur_menu[choice]    elif choice == "b":        if parrent_menu:            cur_menu = parrent_menu.pop()    else:        print("输入错误，请重新输入")