三级目录

思路：

1.变量存放：由于本次数据有键值对的相关性，因此选用字典来存储变量

2.采用函数方式，首先建立输出一级菜单，二级菜单，三级菜单函数

3.显示逻辑：分不同的情况显示不同级菜单

# encoding:utf-8
dict = {
    '北京': {
        '朝阳': ['水立方', '巢'],
        '海淀': ['清华', '北大'],
        '昌平': ['天安门', '公主坟']
    },
    '上海': {
        '沙河': ['同济大学'],
        '天通苑': ['aa'],
        '回龙观': ['bb']
    },
    '西安': {
        '高新': ['锦业一路'],
        '雁塔': ['边家村'],
        '新城': ['革命公园']
    }
}
firstmenu=[]
secondmenu=[]

def menu2():
    print(dict.keys())
    print(list(dict.keys()))
    print(dict['北京'].keys())
    print(dict['上海'].keys())
    print(dict['北京']['海淀'])
    print(dict['北京']['海淀'][0])


def show_firstmenu():
    global firstmenu
    firstmenu = list(dict.keys())
    print('--------firstmenu--------')
    for item in firstmenu:
        print(firstmenu.index(item)+1,item)
    print('请选择进入下一级目录，或输入q(quit)退出')
    # print(firstmenu)
    return firstmenu


def show_secondmenu(args):
    global secondmenu
    arg1=firstmenu[args-1]
    secondmenu=list(dict[arg1].keys())
    print('---------secondmenu-------')
    for item in secondmenu:
        print(secondmenu.index(item)+1,item)
    print('请选择，或输入b(back)返回上级菜单，或输入q(quit)退出')
    return secondmenu

def show_thirdmenu(args,args1):
    S1=firstmenu[args-1]
    S2=secondmenu[args1-1]
    thirdmenu=dict[S1][S2]
    print('---------thirdmenu---------')
    for item in thirdmenu:
        print(thirdmenu.index(item)+1,item)
    print('最后一级目录，请输入b(back)返回上级菜单，或输入q(quit)退出')


def operate_menu():
    while True:
        show_firstmenu()
        firstInput = input('>>:')
        if firstInput == 'q':
            break
        elif firstInput.isdigit():
            firstInput=int(firstInput)
            if firstInput>0 and firstInput<=3:
                while True:
                    show_secondmenu(firstInput)
                    secondInput=input('>>:')
                    if secondInput=='q':
                        exit()
                    elif secondInput=='b':
                        show_firstmenu()
                        break
                    elif secondInput.isdigit():
                        secondInput=int(secondInput)
                        if int(secondInput)>0 and int(secondInput)<=3:
                            while True:
                                show_thirdmenu(firstInput,int(secondInput))
                                third_Input=input(">>:")
                                if third_Input=='q':
                                    exit()
                                elif third_Input=='b':
                                    show_secondmenu(firstInput)
                                    break
                                else:
                                    print('非法输入')
                        else:
                            print('没有该选项，请重新输入')
                    else:
                        print('非法输入')
            else:
                print('没有该选项，请重新输入')
        else:
            print('非法输入')



operate_menu()