1 citys = {
 2     '江苏省':{'南京市':['秦淮区','玄武区','浦口区']},
 3     '河南省':{'郑州市':['二七区','金水区']},
 4     '北京市':{'朝阳区':['朝阳区派出所'],'海淀区':['海淀区派出所']}
 5 }
 6 
 7 exit_flag = False
 8 while not exit_flag:
 9     for i in citys:
10         print(i)
11     choice = input("请输入你的选则1:")
12     if choice == 'q':
13         print("欢迎您下次使用！！！")
14         exit_flag = True
15     elif citys.get(choice):
16         while not exit_flag:
17             for j in citys[choice]:
18                 print(j)
19             choice2 = input("请输入你的选则2:")
20             if choice2 == 'q':
21                 print("欢迎您下次使用！！！")
22                 exit_flag = True
23             elif choice2 == 'b':
24                 break
25             elif citys[choice].get(choice2):
26                 while not exit_flag:
27                     for k in citys[choice][choice2]:
28                         print(k)
29                     choice3 = input("返回上一级菜单或者退出:")
30                     if choice3 =='q':
31                         print("欢迎您下次使用！！！")
32                         exit_flag = True
33                     elif choice3 == 'b':
34                         break
35                     else:
36                         print("无效输入，请重新输入！！！")
37             else:
38                 print("无效输入，请重新输入！！！")
39     else:
40         print("无效输入，请重新输入！！！")