While循环检查有效的用户输入？

Question

Python新手非常抱歉，我确信这是一个愚蠢的问题，但是我似乎无法在一个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 

上面的打印输出到控制台：

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-循环应该在用户输入“y”或“n”时结束，但我不确定如何做到这一点。我在这里做错什么了？

注意：这个挑战要求我同时使用!=运算符和loop_condition

Answer 1

最简单的解决方案是在循环开始之前在初始化一些变量：

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=""

while条件语句的意思是，只要choice变量为false——没有任何值意味着choice=''，则继续循环 如果选项有任何值，则继续进入循环体并检查 特定输入的值，如果输入不满足所需的值 然后再次将选项变量重置为False值以继续提示用户 直到提供正确的输入

Answer 2

你可以用这个条件

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 3

较短的解决方案

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

关于您的代码，您可以添加一些打印内容，如下所示：

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，在代码中有一个第一步，问题出现，您的答案初始化choice的值。这就是你做错的地方。

具有!=和loop_condition的解

如果必须同时使用!=运算符和loop_condition，则应编写代码：

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

然而，在我看来，赛博的解决方案和我的更短的解决方案都更优雅（即更Python）。