关于python：while循环检查有效的用户输入？

While loop to check for valid user input?

本问题已经有最佳答案，请猛点这里访问。

这里的python菜鸟非常抱歉，我确定这是一个愚蠢的问题，但在一个要求我使用while循环检查有效用户输入的教程中，我似乎无法解决以下挑战。

(使用python2.7)

这是我的代码，但不能正常工作：

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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

以上内容打印到控制台：

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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，但我不知道该如何做。我在这里做错什么了？

注：挑战要求我同时使用!=运算符和loop_condition运算符。

你可以使用这个条件

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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:")

较短的解决方案

1 2	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，您可以按如下方式添加一些打印：

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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：

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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，代码中有一个第一步，问题出现，您的答案初始化choice的值。这就是你所做的错事。

使用!=和loop_condition的解决方案

如果必须同时使用!=运算符和loop_condition运算符，则应编码：

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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较短的解决方案都更优雅(即，更多的Python)。