Python程序調試：無限循環

Question

背景： 對於我的計算機科學課，我們被要求創建一個程序來幫助小學的孩子學習基礎數學。
他們會選擇他們想要學習的操作（加法，減法，乘法或除法），或者選擇隨機的，隨機選擇這些操作之一。
一旦選擇了一個操作，用戶將被問到一個問題，然後輸入答案，如果正確的程序會問另一個問題，最多4個問題總數，然後程序將返回菜單。
如果答案不正確，它會要求用戶再次輸入答案，最多三次，如果答案仍然不正確，將顯示正確的答案，則會提出另一個問題（如果4個問題定額是如果沒有其他問題，則返回到菜單。

問題： 我已經寫出所有內容，並且當我在IDLE中運行程序時，一切看起來都在工作，但是在出於某種原因選擇某個操作之後，程序停留在無限循環中，並且不會返回到已經詢問了4個問題之後的菜單。
我第一次使用for循環來滿足4個問題的配額，並且沒有工作，所以然後我嘗試了一個while循環，它讀取while x<4: etc etc，在while循環之前將x定義爲x = 0，然後在函數添加結束時x=x+1。

再次從閱讀代碼，它似乎應該爲每個功能工作，但運行後，我仍然陷入無限循環。

繼承人的代碼：

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()` 

預先感謝您的任何援助，在這裏任何人都可以提供！

Answer 1

您需要將raw_input置於while循環內。

更改主這樣：

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." 

這裏的問題是，raw_input被調用一次，while循環之前。但是，它再也沒有被召喚過。相反，循環會繼續，但它會繼續使用與raw_input第一次（也是唯一）調用時檢索到的值相同的selection值。

另外，在main函數的末尾不需要quit()。你可以讓函數返回。雖然這與你的bug無關。

Answer 2

這將基於隨機數和操作產生問題。

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()