While循环检查有效的用户输入

Question

Python新手在这里很抱歉，我确定这是一个愚蠢的问题，但我似乎无法解决在教程中要求我使用while循环来检查有效用户输入的以下挑战。

(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 

以上输出到控制台:

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。我哪里做错了?

注意:挑战要求我同时使用!=操作符和loop_condition

Answer 1

您可以使用

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

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

对于您的代码，您可以添加如下打印:

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) 

正如您所看到的，在您的代码中有第一步出现了问题，并且您的答案初始化了choice的值。这就是你做错的地方。

含!=和loop_condition的溶液

如果您必须同时使用!=和loop_condition操作符，那么您应该编写:

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的解决方案和我的更短的解决方案都更优雅(即更python化)。

Answer 3

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=""

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= "——"，那么循环继续#如果选项有任何值，则继续进入循环体并进行检查如果输入不满足所需值，则为特定输入的值然后将选项变量再次重置为False值以继续提示用户直到提供正确的输入