听取了Alex老师的话，程序里面尽量用英文，本人编程小白，英语菜鸟，英语不会的地方有用中文表示了，显得代码有些乱，不足之处请多多指教！
catalog = { #在此定义一个三级菜单
"food":{ "fruit":["apple","pear","litchi","banana","watermelon"],
"vegetable":["potato","pumpkin","leek","spinach","cowpea"],
"dessert":["cake","cookie","chocolate","butter","ice cream"]},
"furniture":{"electric":["television","washing machine","freezer","microwave oven"],
"wood":["door","table","bed","cabinet","safa"],
"vehicle":["bicycle","motorcycle","car"]},
"year":{"season":["spring","summer","autumn","winter"],
"month":["January","February","March","April","May","June","July","August","September","October","November","December"],
"festival":["spring festival","april fool's day","Labour Day","valentine's say","Christmas"] }
}
print("+-------------------------+") #打印菜单选项栏
print("+---see the catalog: C---+")
print("+---quit the catalog: Q---+")
print("+---Back up : B---+")
print("+-------------------------+")
temp = True #定义一个用于可随时终止循环的变量
def firt_catalog(first_level): #定义一级目录菜单选项格式
if first_level.lower() == "q": #系统在打印了根目录时，用户输入Q，则直接返回False，将false传递while循环的temp中，终止循环退出程序
return False
elif first_level.lower() == "b": #用户输入B之后，返回上一层菜单，因为最初为根目录。打印提示根目录
print("已经是根目录了！")
return False
else: #如果用户输入的是一级菜单的选项，则打印对应的二级菜单
for each2 in catalog[first_level]:
print(each2 + ",", end="")
print("\nselect level 2 catalog or other choose:")
second_level = input("pleace choose:") #用户做出选择
second_catalog(first_level,second_level) #跳转到二级菜单选择函数中，并将用户选择结果传递到二级菜单选项函数
def second_catalog(first,second): #定义二级菜单选项函数
if second.lower() == "q":
return False
elif second.lower() == "b": #如果用户输入B，则返回上级目录
for each in catalog: #打印上级目录
print(each + ",", end="")
print("\nselect level 1 catalog or other choose:")
first_level = input("pleace choose:")
firt_catalog(first_level) #打印完上级目录之后，因为用户又返回到了一级目录，所以此处又去调用一级目录菜单选择函数
else: #如果用户输入二级目录菜单的元素，则打印该元素下的三级目录菜单
for each3 in catalog[first][second]:
print(each3 + ",", end="")
print("\nselect level 3 catalog or other choose:")
third_choose = input("pleace choose:")
third_catalog(first,second,third_choose) #进入三级目录菜单选择函数
def third_catalog(first,second,third): #定义一个三级目录菜单
if third.lower() == "q":
return False
elif third.lower() == "b":
for each2 in catalog[first]:
print(each2 + ",", end="")
print("\nselect level 2 catalog or other choose:")
second_level = input("pleace choose:")
second_catalog(first,second_level)
else:
return False
user_choose = input("pleace choose:") #用户根据系统提示的选项卡做出选择
while temp: #此处用一个变量作为循环的判断条件，当用户退出后，或者选择了第三级目录菜单则直接修改变量值，用于终止循环
if user_choose.lower() == "c":
for each in catalog:
print(each + ",", end="")
print("\nselect level 1 catalog or other choose:")
first_level = input("pleace choose:")
temp = firt_catalog(first_level)
elif user_choose.lower() == "b":
print("已经是根目录了！")
temp = False
else:
temp = False