如何让while循环适配quit的所有大小写输入以正常终止？

编写了一个用while循环询问披萨配料的程序，仅当输入小写"quit"时能终止循环，但输入"Quit"、"QUIT"等任意大小写组合时无法正常终止。原代码如下：

order = "\nWhat topping do you want? "
response = "\nWe will add that topping to your pizza. Enter 'quit' to finish ordering toppings. "
topping = ""

while topping != "quit":
    topping = input(order)
    if topping != "quit":
        print(response)

解决方案 #

核心思路是将用户输入的文本统一转换为小写（或大写）后再与目标字符串比较，忽略输入的大小写差异。

修改后的代码 #

order = "\nWhat topping do you want? "
response = "\nWe will add that topping to your pizza. Enter 'quit' to finish ordering toppings. "
topping = ""

# 将输入转换为小写后判断终止条件
while topping.lower() != "quit":
    topping = input(order)
    # 同样转换为小写判断，避免错误输出提示信息
    if topping.lower() != "quit":
        print(response)

说明 #

• 调用字符串方法lower()，把用户输入的topping转为全小写格式，这样无论输入"Quit"、"QUIT"还是其他大小写组合，都会被统一处理为"quit"，从而正确触发循环终止逻辑。
• 两处判断都使用lower()，避免出现用户输入非小写"quit"时，先输出提示信息再终止循环的逻辑漏洞。

也可以使用upper()方法实现相同效果，只需将目标字符串改为"QUIT"：

order = "\nWhat topping do you want? "
response = "\nWe will add that topping to your pizza. Enter 'quit' to finish ordering toppings. "
topping = ""

while topping.upper() != "QUIT":
    topping = input(order)
    if topping.upper() != "QUIT":
        print(response)

内容的提问来源于stack exchange，提问作者Hazel P