Python学分校验程序故障求助：始终输出‘Out of range’问题排查

程序要求：当输入的学分不在0、20、40、60、80、100、120范围内时，显示‘Out of range’。

我创建了包含合法学分值的列表，再将输入的三个学分变量存入另一个列表，尝试用if语句判断变量是否在合法列表中，但程序始终输出‘Out of range...’；改用while循环时，会重复输出总和7次。不知道怎么修复，求解答。

def main():
    a = [0, 20, 40, 60, 80, 100, 120]
    try:
        userPass = int(input("Enter pass credits: "))
        userDefer = int(input("Enter defer credits: "))
        userFail = int(input("Enter fail credits: "))
    except:
        print("Invalid number.")
    total = userFail + userPass + userDefer
    aValues = [ userPass, userFail, userDefer ]
    if aValues in a:
        print(total)
    else:
        print("Out of range. Try again")
    if total > 120:
        print("Total incorrect")
        repeat()
    else:
        if userPass >= 120:
            print("This student has progressed.")
            repeat()
        elif userPass >= 100 and total == 120:
            print("This student is trailing.")
            repeat()
        elif userFail <= 60 and total == 120:
            print("This student did not progress(module retreiver).")
            repeat()
        elif userPass <= userFail:
            print("This students program outcome is exclude.")
            repeat()
        else:
            print("incorrect. Try again.")
            repeat()
            
def repeat():
    choice = int(input("If you would like to quit type 1 or test another student write 2: "))
    if choice != 1 and choice != 2:
        repeat()
    else:
        while choice == 2:
            main()
        while choice == 1:
            break
        print("Thank you.")

main()

1. 核心错误：范围判断逻辑完全错误 #

你写的if aValues in a:是在判断整个三元素列表是否是合法列表a中的元素，但a里都是单个数值，这永远不会成立，所以才会一直输出"Out of range"。

正确逻辑是检查每个输入的学分是否都在合法列表中，可以用all()函数简化判断：

# 替换原判断代码
valid = all(credit in a for credit in aValues)
if valid:
    print(total)
else:
    print("Out of range. Try again")

2. 异常处理后的变量未定义问题 #

如果输入非整数触发except块，userPass、userDefer、userFail会未定义，后续代码引用会直接报错。需要在异常处理后终止当前main()执行：

try:
    userPass = int(input("Enter pass credits: "))
    userDefer = int(input("Enter defer credits: "))
    userFail = int(input("Enter fail credits: "))
except:
    print("Invalid number.")
    return  # 直接返回，避免后续报错

3. repeat()函数循环逻辑错误 #

当选择2时，while choice == 2:会无限调用main()，因为choice值不会更新，导致重复执行。改成单次调用后重新进入选择流程即可：

def repeat():
    choice = int(input("If you would like to quit type 1 or test another student write 2: "))
    if choice == 1:
        print("Thank you.")
    elif choice == 2:
        main()
    else:
        print("Invalid choice, try again.")
        repeat()

4. 其他优化点 #

• 合法学分用集合存储，查询速度更快：VALID_CREDITS = {0,20,40,60,80,100,120}
• 修复拼写错误：module retreiver改为module retriever，students改为student's
• 把范围检查放在总和计算之前，避免无效运算

VALID_CREDITS = {0, 20, 40, 60, 80, 100, 120}

def main():
    try:
        userPass = int(input("Enter pass credits: "))
        userDefer = int(input("Enter defer credits: "))
        userFail = int(input("Enter fail credits: "))
    except ValueError:
        print("Invalid number.")
        repeat()
        return

    # 检查每个学分是否合法
    if not all(credit in VALID_CREDITS for credit in [userPass, userDefer, userFail]):
        print("Out of range. Try again")
        repeat()
        return

    total = userPass + userDefer + userFail
    if total > 120:
        print("Total incorrect")
        repeat()
        return
    elif total != 120:
        print("Total must be 120. Try again.")
        repeat()
        return

    # 判断学生进度
    if userPass >= 120:
        print("This student has progressed.")
    elif userPass >= 100:
        print("This student is trailing.")
    elif userFail <= 60:
        print("This student did not progress(module retriever).")
    elif userPass <= userFail:
        print("This student's program outcome is excluded.")
    else:
        print("Incorrect input. Try again.")
    
    repeat()
            
def repeat():
    try:
        choice = int(input("If you would like to quit type 1 or test another student write 2: "))
    except ValueError:
        print("Invalid input, please enter 1 or 2.")
        repeat()
        return
    
    if choice == 1:
        print("Thank you.")
    elif choice == 2:
        main()
    else:
        print("Invalid choice, try again.")
        repeat()

main()

内容的提问来源于stack exchange，提问作者A C