Python程序调试：无限循环

Question

背景： 在我的计算机科学课上，我们被要求创建一个程序来帮助小学生学习基础数学。
他们会选择他们想要学习的运算（加法、减法、乘法或除法），或者选择随机，随机选择这些运算之一。
一旦选择了某个操作，就会询问用户一个问题，然后输入答案，如果正确，程序会询问另一个问题，总共最多 4 个问题，然后程序会返回到菜单。
如果答案不正确，则要求用户重新输入答案，最多3次，如果答案仍然不正确，则会显示正确答案，然后会询问另一个问题（如果未达到4个问题的配额） ）或如果没有其他问题则返回菜单。

问题： 我已经写好了所有内容，当我在 IDLE 中运行程序时，一切似乎都正常工作，但是在由于某种原因选择了一个操作后，程序陷入无限循环，并且在询问 4 个问题后不会返回到菜单。
我首先使用 for 循环来满足 4 个问题的配额，但这不起作用，所以然后我尝试了一个 while 循环，它读取 while x<4: etc etc，将 x 定义为 x=0 之前while 循环，然后在函数末尾添加 x=x+1。

再次阅读代码，它似乎应该适用于每个函数，但运行后我仍然陷入无限循环。

代码如下：

def show_instructions():
    """
    Displays a greeting to the user and provides instructions on how to use the
    program.        [PURPOSE]
    """
    print " "
    print "-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-"
    print "                             Math Mania"
    print " "
    print "Welcome to Math Mania! This program is designed to help you learn basic"
    print "math skills in addition, subtraction, multiplication, and division."
    print "-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-"
    print " "
    print "To learn a skill, type the first letter of that skill."
    print " "
    print "a for addition"
    print "s for subtraction"
    print "m for multiplication"
    print "d for division"
    print "r for random"
    print "q to quit"
    print " "


def add():
    """
    generates display two random numbers and sums them, then prompts the user
    to input the correct sum, if the input is incorrect, it prompts the user
    to try again.
    [PURPOSE]
    """

    x=0
    while x<4:
        num1 = random.randint(1,20)
        num2 = random.randint(1,20)
        print num1, "+", num2, '= ?'
        answer = input ('Enter your answer: ')
        count1=0
        while answer != num1+num2 and count1<3:
            count1=count1 +1
            print 'Incorrect, please try again.'
            print
            print num1, '+', num2, '= ?'
            answer = input ('Enter your answer: ')
        if count1==3:
            print "Sorry, that's incorrect."
            print "The correct answer is ",num1+num2 
        else:
            print "That's correct!"
        print
        x=x+1



def sub():
    """
    generates and displays two random numbers and subtracts the smaller of the
    two from the larger one. It then prompts the user to input the correct
    answer, if the input is incorrect, it prompts the user to try again.
    [PURPOSE]
    """
    x=0
    while x<4:
        num1 = random.randint(1,20)
        num2 = random.randint(1,20)
        if num1>num2:
            print num1, "-", num2, '= ?'
            answer = input('Enter your answer: ')
            count1=0
            while answer != num1 - num2 and count1<3:
                count1=count1+1
                print 'Incorrect, please try again.'
                print
                print num1, "-", num2, '= ?'
                answer = input ('Enter your answer: ')
            if count1==3:
                print "Sorry, that's incorrect."
                print "The correct answer is ",num1-num2
            else:
                print "That's correct!"
            print
            x=x+1
        else:
            print num2, "-", num1, '= ?'
            answer = input ('Enter your answer')
            count1=0
            while answer!= num2-num1 and count1<3:
                count1=count1+1
                print 'Incorrect, please try again.'
                print
                print num2, "-", num1, '= ?'
                answer = input ('Enter your answer: ')
            if count1==3:
                print "Sorry, that's incorrect."
                print "The correct answer is ",num2-num1
            else:
                print 'Thats correct!'
            print
            x=x+1

def mult():
    """
    generates and displays two random numbers and finds the product of the two.
    It then prompts the user to input the correct product of the two numbers, if
    the input is incorrect, it prompts the user to try again.
    [PURPOSE]
    """
    x=0
    while x<4:
        num1 = random.randint(1,20)
        num2 = random.randint(1,20)
        print num1, "x", num2, '= ?'
        answer = input ('Enter your answer: ')
        count1=0
        while answer != num1*num2 and count1<3:
            count1=count1+1
            print 'Incorrect, please try again.'
            print
            print num1, 'x', num2, '= ?'
            answer = input ('Enter your answer: ')
        if count1==3:
            print "Sorry, that's incorrect."
            print "The correct answer is ", num1*num2
        else:
            print "That's correct!"
        print
        x=x+1


def div():
    """
    generates and displays the quotient of two numbers, and then prompts the
    user to input the correct answer, if the input is incorrect, it then prompts
    the user to try again.
    [PURPOSE]
    """

    x=0
    while x<4:
        num1 = random.randint(1,20)
        num2 = random.randint(1,20)

        while (num1%num2!=0):
            num2 = random.randint(1,20)
            num1 = random.randint(1,20)
        print num1, "/", num2, '= ?'
        answer = input ('Enter your answer: ')


        count1=0
        while answer != num1/num2 and count1<3:
            count1=count1 +1
            print 'Incorrect, please try again.'
            print num1, '/', num2, '= ?'
            answer = input ('enter your answer:')
        if count1==3:
            print "Sorry, that's incorrect."
            print "The correct answer is ",num1/num2 
        else:
            print "That's correct!"
        print
        x=x+1
def rand():
    """
    picks a arithmetic function at random for the user to to try
    [PURPOSE]
    """
    num=random.randint(1,4)
    if num==1:
        add()
    if num==2:
        sub()
    if num==3:
        mult()
    if num==4:
        div()

def main():
    """
    main function that brings it all together
    [PURPOSE]
    """
    show_instructions()
    selection = raw_input ('Please select the skill you want to learn: ')
    while selection != "q":
        if selection == "a":
            add()
        elif selection == "s":
            sub()
        elif selection == "m":
            mult()
        elif selection == "d":
            div()
        elif selection == "r":
            rand()
    print "The program will now quit."
    quit()
main()`

提前感谢您提供的任何帮助！

Answer 1

您需要将 raw_input 放入 while 循环中。

将 main 更改为：

def main():
    """
    main function that brings it all together
    [PURPOSE]
    """
    show_instructions()
    selection = None
    while selection != "q":
        selection = raw_input ('Please select the skill you want to learn: ')
        if selection == "a":
            add()
        elif selection == "s":
            sub()
        elif selection == "m":
            mult()
        elif selection == "d":
            div()
        elif selection == "r":
            rand()
    print "The program will now quit."

这里的问题是 raw_input 在 while 循环之前被调用一次。然而，它再也没有被调用过。相反，循环将继续，但它将继续使用在第一次（也是唯一一次）调用 raw_input 时检索到的相同 selection 值。

此外，您不需要在 main 函数末尾使用 quit() 。你可以让函数返回。虽然这与你的错误无关。

Answer 2

这将产生基于随机数和运算的问题。

from string import lower
from operator import add, sub, mul
from random import randint, choice

ops = { '+': add, '-': sub, '*': mul}
MAXTRIES = 2

def doprob():
    op = choice('+-*')
    nums = [randint(1,10), randint(1,10)]
    nums.sort();nums.reverse()
    ans = apply(ops[op], nums)
    pr = '%d %s %d = ' % (nums[0], op, nums[1])
    oops = 0
    while True:
        try:
            if int(raw_input(pr)) == ans:
                print 'correct'
                break
            if oops == MAXTRIES:
                print 'answer\n%s%d'%(pr, ans)
            else:
                print 'incorrect... try again'
                oops = oops + 1
        except (KeyboardInterrupt, EOFError, ValueError):
            print 'invalid input... try again'

def main():
    while True:
        doprob()
        try:
            opt = lower(raw_input('Again? ' ))
        except (KeyboardInterrupt, EOFError):
            print ; break
        if opt and opt[0] == 'n':
            break

if __name__ == '__main__':
    main()