Python_三级菜单的实现

#多级菜单
三级菜单
可以依次选择进入各子菜单

china_ditie = {
    "北京": {
        "一号线": ["四惠", "大望路", "天安门", "西单"],

        "二号线": ["北京站", "朝阳门", "东直门", "西直门"],

        "三号线": ["国贸", "三元桥", "知春路", "巴沟"]

    },
    "上海": {
        "四号线": ["徐家汇", "人民广场", "延长路", "共康路", "呼兰路"],

        "五号线": ["东昌路", "静安寺", "江苏路", "虹桥火车站"],

        "六号线": ["宝山路", "赤峰路", "曹阳路", "虹桥路", "宜山路"]

    },
    "广州": {
        "七号线": ["东山口", "农讲所", "烈士陵园", "公园前", "体育西路"],

        "八号线": ["黄边", "纪念堂", "三元里", "白云公园"],

        "九号线": ["沙河顶", "北京路", "一德路", "文化公园"]

    },
    "深圳": {
        "一号线": ["高新园", "桃园", "白石洲", "华侨城"],

        "四号线": ["白石龙", "明乐", "少年宫", "红山"],

        "五号线": ["大学城", "兴东", "西里", "深圳北站"]

    },

}#程序开始
start = True
city_list=[]
xian_list=[]
print("\033[31;1m欢迎乘坐地铁\033[1m".center(40,'='))
while start:
    for i,cin in enumerate(china_ditie,1):
        print(i,cin)
        city_list.append(cin)
    print("退出\033[31;1m按q\033[1m")
    print("".center(36,'='))
    cchoice=input("选择你要查询的城市：")
    print("".center(36,'='))
    if cchoice=='q' or cchoice=='Q':
        break
    if cchoice.isdigit():
        cchoice=int(cchoice)
        if cchoice<=len(city_list) and cchoice>0:
            while start:
                for j,cin2 in enumerate(china_ditie[city_list[cchoice-1]],1):
                    xian_list.append(cin2)
                    print(j,cin2)
                cchoice2 = input("选择你要查询的线路：")
                print("".center(36,'='))
                if cchoice2 == 'b' or cchoice2 == 'B':
                    break
                if cchoice2.isdigit():
                    cchoice2 = int(cchoice2)
                    if cchoice2 <= len(xian_list) and cchoice2 > 0:
                         for k,cin3 in enumerate(china_ditie[city_list[cchoice-1]][xian_list[cchoice2-1]],1):
                             print(cin3)
                    else:
                        break
                else:
                    break
        else:
            break
    else :
        break