python: practice three-level manu

menu={'china':{'jx_province':{'sr_manicipality':{'yiyang_country':['qinghu_town','guifeng_town','wangli_town']},},},

             'American':{'wathton.dc':{'ei':{'mi':['dei','dei','bue']},},},

            'Britian':{'london':{'ei':{'mi':['dei','dei','bue']},},},

            'Rusian':{'mosque':{'ei':{'mi':['dei','dei','bue']}}}

            }

back_flag=False

exit_flag=False

while not back_flag and not exit_flag:
    for key,v in enumerate(menu,1):

        print(key,v)

    choice=input('>>:').strip()

    if choice in menu:

         while not back_flag and not exit_flag:

               for key2,v2 in enumerate(menu[choice]):

                      print(key2,v2)

               choice2=input('2>>:').strip()

               if choice2=='b':

                    back_flag=True

               if choice2=='q':

                    exit_flag=True

                    break

               if choice2 in menu[choice]:

                     while not back_flag and not exit_flag:

                          for key3,v3 in enumerate(menu[choice][choice2]):

                                print(key3,v3)

                          choice3=input('3>>').strip()

                          if choice3=='b':

                               back_flag=True

                          if choice3=='q':

                              exit_flag=True

                              break

                          if choice3 in menu[choice][choice2]:

                                for key4,v4 in enumerate(menu[choice][choice2][choice3],1):

                                        print(key4,v4)

                                choice5=input('5>>').strip()

                                print('This is last level')

                                if choice5=='b':

                                      back_flag=True

                                if choice5=='q':

                                     exit_flag=True

                                     break

                                else:
                                   back_flag=True



                          else:

                               back_flag=False

                     else:

                         back_flag=Fals