新手：python里面while循环2——代码优化

# -*- coding:utf-8 -*-
# __author: Andy Liu
# Date: 2023/3/2
menu = {
    "lucky_shop": {
        "fruit": {
            "banana": {"banana need 8yuan": {"This is the last layer, please return": {None}}},
            "apple": {"apple need 7yuan": {"This is the last layer, please return": {None}}},
            "tangerine": {
                "Sugar Tachibana need 5yuan": {"This is the last layer, please return": {None}},
                "Citrus need 8yuan": {"This is the last layer, please return": {None}}

            }
        },
        "stationery": {
            "pencil": {"pencil need 2yuan": {"This is the last layer, please return": {None}}},
            "pen": {"pen need 5yuan": {"This is the last layer, please return": {None}}},
            "notebook": {
                "small need 1yuan": {"This is the last layer, please return": {None}},
                "middle need 2yuan": {"This is the last layer, please return": {None}},
                "big need 3yuan": {"This is the last layer, please return": {None}}
            }
        },
        "kitchen": {
            "knife": {"knife need 10yuna": {"This is the last layer, please return": {None}}},
            "wok": {
                "middle need 20yuan": {"This is the last layer, please return": {None}},
                "big need 25yuan": {"This is the last layer, please return": {None}}
            },
            "spatula": {"spatula need 13yuan": {"This is the last layer, please return": {None}}}
        }
    },
    "seven_eleven": {None},
    "super_market": {None}
}


quit_flag = False
current_layer = menu
previous_layer = []

while not quit_flag:
    print("[press 'b' return to the previous layer.]")
    print("[press 'q' return to exit.]")
    while not quit_flag:
        print("-----------")
        for key in current_layer:
            print(key)
        choice = input(">> ").strip()
        if choice in current_layer:
            previous_layer.append(current_layer)
            current_layer = current_layer[choice]
        elif choice == "b":
            if previous_layer:
                current_layer = previous_layer.pop()
        elif choice == "q":
            quit_flag = True
        else:
            print("invalid input!")

print("Welcome again!")