Python 编程循环

Question

我正在做一个任务，我必须针对不同的主题进行测验。这是我目前的代码。

print("Hello and welcome to Shahaad's quiz!") #Introduction
name = input("What is your name? ")
print("Alright", name,", these will be today's topics:")
print("a) Video Games")
print("b) Soccer")
print("c) Geography") 
choice = input("Which topic would you like to begin with?")
if choice == 'video games' or choice == 'Video Games' or choice == 'Video games' or choice == 'a)':
    print("You picked Video Games.")
print("Question number one:")
print("What is the most popular FPS (First Person Shooter) game?")
print("a) Call of Duty")
print("b) Battlefield")
print("c) Grand Theft Auto 5")
print("d) Counter Strike")
answer = input("Your answer:")
guessesTaken = 0
if answer == 'Call Of Duty' or answer == 'Call of duty' or answer == 'Call of duty' or answer == 'a)' or answer == 'call of duty':
    print("You are correct!")
else: 
    guessesTaken = guessesTaken + 1
    print("Incorrect!")
    print("You have", guessesTaken, "guess left!")

我正在努力做到这一点，以便如果他们回答错误，他们将有另一个机会回答这个问题。现在一旦他们弄错了，他们就不能再打字了。谢谢！

Answer 1

您应该按照@BartoszKP 的说法，使用while 循环来检查用户是否输入了有效的输入。

话虽如此，我有一些建议可以提高代码的可读性。 而不是这个

if choice == 'video games' or choice == 'Video Games' or choice == 'Video games' or choice == 'a)':
    print("You picked Video Games.")

您可以利用str().lower() 方法：

if choice.lower() == 'video games' or choice == 'a':
    print('You picked Video Games.")

lower() 方法将所有字母转换为小写。

关于 while 循环，我不喜欢使用标志变量——它在代码中添加了一个不需要的额外变量。相反，您可以使用break

while True:
    choice = input('Which topic would you like to begin with?')
    if choice.lower() == 'video games' or 'a':
        print('You picked Video Games.')
        break #This breaks out of the while loop, and continues executing the code that follows the loop

另一种解决方案是在while 循环之前定义choice 变量，并运行它直到输入符合您的要求：

choice = input('Which topic would you like to begin with?')
while choice.lower() != 'video games' and choice != 'a':
    print('Please pick a valid option')
    choice = input('Which topic would you like to begin with?')
print('You picked "{}".'.format(choice))

如果您希望能够在不同的选项之间进行选择，可以通过检查输入字符串是否是列表中的一项来进一步改进代码：

valid_options = ['video games', 'a', 'software', 'b', 'cartoons', 'c']
choice = input('Which topic would you like to begin with?')
while choice.lower() not in valid_options:
    print('Please pick a valid option')
    choice = input('Which topic would you like to begin with?')
print('You picked "{}".'.format(choice))

输出：

Which topic would you like to begin with?Movies
Please pick a valid option
Which topic would you like to begin with?vIdeO gaMes
You picked "vIdeO gaMes".

Which topic would you like to begin with?software
You picked "software".

如果您使用 Python 2.x，您还应该考虑使用 raw_input() 而不是 input()。请参阅this 相关的 SO 问题以了解原因。

Answer 2

这是一个简单且经常遇到的问题。该解决方案通常适合这种情况：

flag = False

while not flag:
    x = input("Get input from the user:")

    if validate(x):
        flag = True
    else:
        print "Input invalid. Try again"

当然应该更改变量名称以适合当前任务（例如flag --> answerCorrect 或类似，x --> answer 等）。