给出所需输入时如何结束while循环？

Question

我的程序接受用户关于他们想要添加的内容的输入。这很好用，但是当它归结为嵌套的 while 循环时就会出现问题，该循环会提示用户是否希望添加更多项目 (y/n)。我希望 y 从头开始​​循环， n 退出循环并继续程序，以及任何其他输入在重新启动 y/n 提示时给出错误。 我似乎无法弄清楚如何摆脱嵌套的 while 循环，如果输入既不是 y 也不是 n，我也无法弄清楚如何抛出错误。我该如何解决这个问题？

elif user_input == "a":
    while True:
        try:
            add_item = input("What item would you like to add? ").lower()
            if not re.match("^[a-z, A-Z]*$", add_item):
                print("ERROR: Only letters A-Z are allowed!")
                continue
            elif len(add_item) < 1 or len(add_item) > 20:
                print("Item name is too long, only a maximum of 20 characters are allowed!")
                continue
            else:
                item_amount = int(input("How many of these would you like to add? "))
                shopping_list[add_item] = item_amount
                print(f"{item_amount}x {add_item.title()} added to the shopping list.\n")
            while True:
                try:
                    add_more = input("Would you like to add more items? (y/n): ").lower()
                    if add_more == "y":
                        break
                    elif add_more == "n":
                        break
                except TypeError:
                    print("ERROR: Expected y or n in return! Try again!.\n")
                    break
        except ValueError:
            print("\nERROR: Amount must be an integer! Try adding an item again!\n")

Answer 1

1. 使用布尔变量（keep_adding 用于下面的代码）来决定 while 循环的终止条件。它将被设置为False iff add_more == "n"

2. 如果用户输入既不是“y”也不是“n”，则使用raise TypeError 到raise error。

3. 如果输入无效，您应该从 except TypeError 中删除 break，以便继续询问“您想添加更多项目吗？（y/n）：”。

elif user_input == "a":
    keep_adding = True
    while keep_adding:
        try:
            add_item = input("What item would you like to add? ").lower()
            if not re.match("^[a-z, A-Z]*$", add_item):
                print("ERROR: Only letters A-Z are allowed!")
                continue
            elif len(add_item) < 1 or len(add_item) > 20:
                print("Item name is too long, only a maximum of 20 characters are allowed!")
                continue
            else:
                item_amount = int(input("How many of these would you like to add? "))
                shopping_list[add_item] = item_amount
                print(f"{item_amount}x {add_item.title()} added to the shopping list.\n")
            while True:
                try:
                    add_more = input("Would you like to add more items? (y/n): ").lower()
                    if add_more == "y":
                        break
                    elif add_more == "n":
                        keep_adding = False
                        break
                    else:
                        raise TypeError
                except TypeError:
                    print("ERROR: Expected y or n in return! Try again!.\n")
        except ValueError:
            print("\nERROR: Amount must be an integer! Try adding an item again!\n")