作业概述：
写一个三级菜单
实现如下功能：
（1）可依次选择进入各子菜单
（2）在每一级按“b”都可以返回上一级，按“q"都可以退出
流程图：
readme：
简介： three_menu.py是显示三级菜单的程序主要功能： 显示一级（区域）、二级（省）、三级菜单（市、区），三级菜单再选泽可以显示市区的人口和面积（为了节省时间，随意指定的），在任意级都可以返回上一级，或者退出
三级菜单和市区的人口和面积用字典表示： China_map={ '华北':{'北京':['东城','西城','朝阳','海淀'],'河北':['保定','邯郸','唐山','海淀']}, '华东':{'上海':['虹桥','徐汇','黄埔','普陀'],'江苏':['南京','苏州','无锡','徐州']}, '华南':{'广东':['深圳','东莞','湛江','佛山'],'海南':['海口','三亚','三沙']} } city_district_info={'东城':[1000,2000],'西城':[1001,2001],'朝阳':[1002,2002],'海淀':[1003,2003],'保定':[1004,2004],'邯郸':[1005,2005], '唐山':[1006,2006],'海淀':[1007,2007],'虹桥':[1008,2008],'徐汇':[1009,2009],'黄埔':[1010,2010],'黄埔':[1011,2011],'南京':[1012,2012],'苏州':[1013,2013], '无锡':[1014,2014],'徐州':[1015,2015],'深圳':[1016,2016],'东莞':[1017,2017],'湛江':[1018,2018],'佛山':[1019,2019],'海口':[1020,2020], '三亚':[1021,2021],'三沙':[1022,2022]}
执行方法： 在cmd下进入three_menu.py文件的路径，然后直接执行python three_menu.py即可
代码：
#coding=utf-8
import sys
China_map={
'华北':{'北京':['东城','西城','朝阳','海淀'],'河北':['保定','邯郸','唐山','海淀']},
'华东':{'上海':['虹桥','徐汇','黄埔','普陀'],'江苏':['南京','苏州','无锡','徐州']},
'华南':{'广东':['深圳','东莞','湛江','佛山'],'海南':['海口','三亚','三沙']}
}
city_district_info={'东城':[1000,2000],'西城':[1001,2001],'朝阳':[1002,2002],'海淀':[1003,2003],'保定':[1004,2004],'邯郸':[1005,2005],
'唐山':[1006,2006],'海淀':[1007,2007],'虹桥':[1008,2008],'徐汇':[1009,2009],'黄埔':[1010,2010],'黄埔':[1011,2011],'南京':[1012,2012],'苏州':[1013,2013],
'无锡':[1014,2014],'徐州':[1015,2015],'深圳':[1016,2016],'东莞':[1017,2017],'湛江':[1018,2018],'佛山':[1019,2019],'海口':[1020,2020],
'三亚':[1021,2021],'三沙':[1022,2022]}
#遍历一级菜单
def one_level_menu():
error_num=1
one_level_menu_dict={}
#print('一级菜单列表：',list(China_map.keys()))
for i in range(len(list(China_map.keys()))):
one_level_menu_dict[i]=list(China_map.keys())[i]
print ('一级菜单dict：',one_level_menu_dict)
while 1:
one_menu_choose=input('请选择Region代号；q:退出系统，b:返回上级菜单')
if one_menu_choose == 'b':
print('最顶层菜单，无法返回')
elif one_menu_choose == 'q':
sys.exit()
elif one_menu_choose in (str(list(one_level_menu_dict.keys()))): #list(one_level_menu_dict.keys())取出one_level_menu_dict字典中的所有的key值形成列表
error_num=1 #输入错误后，如果再输入正确，那么错误数重新计算
two_level_menu(one_level_menu_dict,one_menu_choose) #调用二级菜单函数，显示二级菜单
elif one_menu_choose not in (str(list(one_level_menu_dict.keys()))):
print('Region代码输入错误，重新输入,第%d次错误' %error_num)
if error_num < 3:
error_num=error_num+1
else:
sys.exit()
#显示二级菜单
def two_level_menu(one_level_menu_dict,one_menu_choose):
error_num=1
two_level_menu_dict={}
Region_name=one_level_menu_dict[int(one_menu_choose)] #区域名字
print ('选择的区域的名字：',Region_name)
#print ('二级菜单list：',list(China_map[Region_name].keys()))
for i in range(len(list(China_map[Region_name].keys()))):
two_level_menu_dict[i]=list(China_map[Region_name].keys())[i]
print ('二级菜单dict:',two_level_menu_dict)
while 1:
two_menu_choose=input('请选择Province代号；q:退出系统，b:返回上级菜单')
if two_menu_choose == 'b': #输入b，退回上级菜单
#print('bbbb')
one_level_menu()
elif two_menu_choose == 'q': #输入q，退出程序
sys.exit()
elif two_menu_choose in (str(list(two_level_menu_dict.keys()))): #list(one_level_menu_dict.keys())取出one_level_menu_dict字典中的所有的key值形成列表
error_num=1 #输入错误后，如果再输入正确，那么错误数重新计算
three_level_menu(one_level_menu_dict,two_level_menu_dict,Region_name,one_menu_choose,two_menu_choose) #调用三级菜单函数，显示三级菜单
elif two_menu_choose not in (str(list(two_level_menu_dict.keys()))):
print('Province代码输入错误，重新输入,第%d次错误' %error_num)
if error_num < 3:
error_num=error_num+1
else:
sys.exit()
#显示三级菜单
def three_level_menu(one_level_menu_dict,two_level_menu_dict,Region_name,one_menu_choose,two_menu_choose):
error_num=1
three_level_menu_dict={}
Province_name=two_level_menu_dict[int(two_menu_choose)] #城市名字
print ('选择的省的名字：',Province_name)
#print ('三级菜单list：',list(China_map[Region_name][City_name]))
for i in range(len(list(China_map[Region_name][Province_name]))):
three_level_menu_dict[i]=list(China_map[Region_name][Province_name])[i]
print ('三级菜单dict:',three_level_menu_dict)
while 1:
three_menu_choose=input('请选择City-District代号；q:退出系统，b:返回上级菜单')
if three_menu_choose == 'b':
two_level_menu(one_level_menu_dict,one_menu_choose)
elif three_menu_choose == 'q':
sys.exit()
elif three_menu_choose in (str(list(three_level_menu_dict.keys()))):
display_city_distrct_info(one_level_menu_dict,two_level_menu_dict,three_level_menu_dict,Region_name,one_menu_choose,two_menu_choose,city_district_info)
elif three_menu_choose not in (str(list(three_level_menu_dict.keys()))):
print('City-District代码输入错误，重新输入,第%d次错误' %error_num)
if error_num < 3:
error_num=error_num+1
else:
sys.exit()
def display_city_distrct_info(one_level_menu_dict,two_level_menu_dict,three_level_menu_dict,Region_name,one_menu_choose,two_menu_choose,city_district_info):
error_num=1
print('美丽的%s欢迎你' %three_level_menu_dict[int(two_menu_choose)])
city_district_name=three_level_menu_dict[int(two_menu_choose)]
total_population=city_district_info[three_level_menu_dict[int(two_menu_choose)]][0]
area=city_district_info[three_level_menu_dict[int(two_menu_choose)]][1]
msg='''%s简介信息：
-----------------------
总人口:%s
总面积:%d
----------End----------''' %(city_district_name,total_population,area)
print(msg)
last_menu_choose=input('请选择代号：q:退出系统，b:返回上级菜单')
if last_menu_choose == 'q':
sys.exit()
elif last_menu_choose == 'b':
three_level_menu(one_level_menu_dict,two_level_menu_dict,Region_name,one_menu_choose,two_menu_choose)
else:
last_again_menu_choose=input('代号输入错误，请选重新输入：q:退出系统，b:返回上级菜单')
if __name__=='__main__':
one_level_menu()