While循环检查有效的用户输入？ [复制]

Question

这里的 Python 新手很抱歉，我确定这是一个愚蠢的问题，但我似乎无法在教程中解决以下挑战，该教程要求我使用 while 循环来检查有效的用户输入。

（使用Python2.7）

这是我的代码，但它不能正常工作：

choice = raw_input('Enjoying the course? (y/n)')
student_surveyPromptOn = True
while student_surveyPromptOn:
    if choice != raw_input('Enjoying the course? (y/n)'):
        print("Sorry, I didn't catch that. Enter again: ")
    else:
        student_surveyPromptOn = False 

上面的内容打印到控制台：

Enjoying the course? (y/n) y
Enjoying the course? (y/n) n
Sorry, I didn't catch that. Enter again: 
Enjoying the course? (y/n) x
Sorry, I didn't catch that. Enter again: 
Enjoying the course? (y/n)  

这显然是不正确的——当用户输入“y”或“n”时，循环应该结束，但我不知道该怎么做。我在这里做错了什么？

注意：挑战要求我同时使用 != 运算符和 loop_condition

Answer 1

你可以使用条件

while choice not in ('y', 'n'):
    choice = raw_input('Enjoying the course? (y/n)')
    if not choice:
        print("Sorry, I didn't catch that. Enter again: ")

Answer 2

更短的解决方案

while raw_input("Enjoying the course? (y/n) ") not in ('y', 'n'):
    print("Sorry, I didn't catch that. Enter again:")

你的代码做错了什么

关于你的代码，你可以添加一些打印如下：

choice = raw_input("Enjoying the course? (y/n) ")
print("choice = " + choice)
student_surveyPromptOn = True
while student_surveyPromptOn:
    input = raw_input("Enjoying the course? (y/n) ")
    print("input = " + input)
    if choice != input:
        print("Sorry, I didn't catch that. Enter again:")
    else:
        student_surveyPromptOn = False

上面打印出来：

Enjoying the course? (y/n) y
choice = y
Enjoying the course? (y/n) n
choice = y
input = n
Sorry, I didn't catch that. Enter again:
Enjoying the course? (y/n) x
choice = y
input = x
Sorry, I didn't catch that. Enter again:
Enjoying the course? (y/n) 

如您所见，在您的代码中出现问题的第一步，您的答案会初始化choice 的值。这就是你做错了。

!= 和 loop_condition 的解决方案

如果您必须同时使用!= 运算符和loop_condition，那么您应该编码：

student_surveyPromptOn = True
while student_surveyPromptOn:
    choice = raw_input("Enjoying the course? (y/n) ")
    if choice != 'y' and choice != 'n':
        print("Sorry, I didn't catch that. Enter again:")
    else:
        student_surveyPromptOn = False

但是，在我看来，Cyber​​ 的解决方案和我的更短的解决方案都更优雅（即更 Pythonic）。

Answer 3

对此非常简单的解决方案是在循环开始之前初始化一些变量：

choice=''

#This means that choice is False now

while not choice:
    choice=input("Enjoying the course? (y/n)")
        if choice in ("yn")
            #any set of instructions
        else:
            print("Sorry, I didn't catch that. Enter again: ")
            choice=""

这个while条件语句的意思是，只要choice变量为假--没有任何值就意味着choice=''--，然后继续#用循环 如果 choice 有任何值，则继续进入循环体并检查 特定输入的值，如果输入不满足要求的值 然后再次将 choice 变量重置为 False 值以继续提示用户 直到提供正确的输入