tertiary menu

need:
Can be selected in turn to enter each submenu
Can go back from any layer to the previous layer
The program can be exited from any level

1  # !/usr/bin/env python3 
2  # -*- coding:utf-8 -*- 
3  ''' 
4  Time:2018/5/3 16:23
 5  File:Three-level menu
 6  Author:ly
 7  ' '' 
8 menu = {
 9      ' Beijing ' :{
 10          ' Haidian ' :{
 11              ' Wudaokou ' :{
 12                  ' soho ' :{},
 13                  ' Netease ' :{},
 14                  ' google ' :{}
 15             },
 16              ' Zhongguancun ' :{
 17                  ' iQiyi ' :{},
 18                  ' Autohome ' : {},
 19                  ' youku ' :{},
 20              },
 21              ' Shangdi ' :{
 22                  ' Baidu ' :{},
 23              },
 24          },
 25          ' Changping ' :{
 26              ' Shahe ' :{
 27                  ' Old Boy ' :{},
28                 ' Beihang ' :{},
 29              },
 30              ' Tiantongyuan ' :{},
 31              ' Huilongguan ' :{},
 32          },
 33          ' Chaoyang ' :{},
 34          ' Dongcheng ' :{},
 35      },
 36      ' Shanghai ' :{
 37          ' Minhang ' :{
 38              " People's Square " :{
 39                  ' Fried Chicken ' :{}
 40              }
 41         },
 42          ' Zhabei ' :{
 43              ' Train Station ' :{
 44                  ' Ctrip ' :{}
 45              }
 46          },
 47          ' Pudong ' :{},
 48      },
 49      ' Shandong ' :{},
 50  }
 51 Current_layer = menu #Current layer 
52  
53 Next_layer = [ menu ] #Next layer 54 
55  
exit_flag = False
 56  
57  while not exit_flag:
 58      for i in Current_layer: 59          print (i)
 60      choice = input( " Please enter your choice|Breturn|Qexit: " ).strip()
 61  
62      if choice in Current_layer: #If in the current layer 
63 Next_layer.append          (Current_layer) #Then add the current layer to the next layer 
64          Current_layer = Current_layer[choice]
 65  
66      if choice == ' b ' .casefold():
 67          if len(Next_layer) ==0:
 68              continue 
69          Current_layer = Next_layer[-1] #Get the previous layer and assign it to the current layer 
70          Next_layer.pop()
 71          # print(Next_layer) 
72  
73      if choice== ' q ' .casefold():
 74          exit_flag = True
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