While循环检查有效的用户输入？[副本]

Question

这里的Python新手非常抱歉，我确信这是一个愚蠢的问题，但在一个教程中，我似乎无法解决以下挑战，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，但它工作不正常：

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 

上述内容打印到控制台：

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)  

这显然是不对的-

注意：挑战要求我同时使用！=运算符和loop_condition

Answer 1

对此，最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=""

while条件语句的意思是，只要选择变量为false-，没有任何值意味着选择=“”-，然后继续循环如果选择有任何值，则继续进入循环体并检查特定输入的值，如果输入未满足要求的值，则再次将选择变量重置为False值以继续提示用户，直到提供正确的输入

Answer 2

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

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：

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，在代码中的第一步，问题出现了，您的答案初始化了选择的值。这就是你做错的地方。

如果必须同时使用= 运算符和循环\u条件然后应编码：

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

然而，在我看来，Cyber的解决方案和我的较短的解决方案都更优雅（即，更具pythonic）。

Answer 3

你可以使用这个条件

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: ")