python 2.7.3 while循环

Question

我是python的新手。 我需要反复循环，要求用户选择一个选项，然后运行命令并重复直到用户选择退出。 如果用户选择任何其他选项，程序必须一直要求他们选择一个值，直到他们选择一个正确的值。 到目前为止，我的计划进展不顺利。 如果可能的话，我想保持原状，如果，elif条件。 有人能够提供帮助吗？ 非常感谢！

print """
How do you feel today?
1 = happy
2 = average
3 = sad
0 = exit program
"""

option = input("Please select one of the above options: ")
while option > 0 or option <=3:
    if option > 3:
        print "Please try again"
    elif option == 1:
        print "happy"
    elif option == 2:
        print "average"
    elif option == 3:
        print "sad"
    else:
        print "done"

Answer 1

break命令将为您退出循环 - 但是，就开始控制流而言，它也不是真正推荐的。 但请注意，用户永远不能输入新值，因此您将陷入无限循环。

也许尝试这个：

running = True

while running:
    option = input("Please select one of the above options: ")
    if option > 3:
        print "Please try again"
    elif option == 1:
        print "happy"
    elif option == 2:
        print "average"
    elif option == 3:
        print "sad"
    else:
        print "done"
        running = False

Answer 2

这是我将如何修改它以实现预期的结果。你在哪里关闭但if和else不应该在循环内:)。

print """
How do you feel today?
1 = happy
2 = average
3 = sad
0 = exit program
"""

option = input("Please select one of the above options: ")
while option >3:
    print "Please try again"
    option = input("Please select one of the above options: ")

if option == 1:
    print "happy"
elif option == 2:
    print "average"
elif option == 3:
    print "sad"
else:
    print "done"

请注意，您可以随时使用break来停止循环

谢谢Ben

Answer 3

import sys
option = int(input("Please select one of the above options: "))
while not option in (0, 1, 2, 3):
    option = int(input("Please select one of the above options: ")
    if option == 0: sys.exit()
    else: print "Please try again"
if option == 1:
        print "happy"
elif option == 2:
        print "average"
elif option == 3:
        print "sad"

逻辑是如果选项不是0,1,2或3，程序会不断要求输入。 如果它在该范围内，则循环结束并打印结果。 如果输入为0，则程序使用sys.exit()结束。

或者，您可以使用字典创建更简单，更短的程序：

import sys
userOptions = {1: 'happy', 2: 'average', 3: 'sad'}
option = int(input("Please select one of the above options: "))
while not option in (0, 1, 2, 3):
    option = int(input("Please select one of the above options: ")
    if option == 0: sys.exit()
    else: print "Please try again"
print userOptions[option]