如果语句没有按预期跳出循环

Question

这是我目前的函数代码（错误可能发生在这里）：

def showAddition():
    print("You have selected: \"Addition\"")
            
    while True:
        last_answer = None
        if last_answer:
            next_num = int(input("Please input another number: "))
            answer = calc.addNums(last_answer, next_num)
        else:
            num1 = int(input("Please enter your first number: "))
            num2 = int(input("Please enter your second number: "))
            answer = calc.addNums(num1, num2)
                
            print(f'Your answer is {answer}')
            continue_prompt = input("Would you like to continue? Y/N\n")
                    
            if continue_prompt.upper() == "Y" or continue_prompt.upper() == "YES":
                last_answer = answer
            else:
                break

我想让它可以让我立即输入另一个数字，能够一个接一个地加数字，不会出错。但是，不知道为什么，循环就是一直重复。即使我在继续提示中输入“no”，它也不会停止。无论是输入“yes”还是“no”，结果都是完全一样的，我搞不懂这是为什么。

Answer 1

如果你假设在询问是否继续时，除了“N”以外的任何回答都意味着这个过程应该继续，那么你可以简化这个过程。

一定要验证数字输入。

举个例子：

class calc:
    @staticmethod
    def addNums(*args):
        return sum(args)

def proceed() -> bool:
    while True:
        yn = input("Do you wish to continue Y/N: ").upper()
        if yn in {"Y", "N"}:
            return yn == "Y"
        print("\aPlease respond with Y or N")

def getint(prompt: str) -> int:
    while True:
        x = input(prompt)
        try:
            return int(x)
        except ValueError:
            print(f"\a'{x}' is not a valid integer")

def showAddition():
    print("You have selected: \"Addition\"")
    total = getint("Please enter your first number: ")
    while True:
        num = getint("Please enter the next value: ")
        total = calc.addNums(total, num)
        print(f"Current {total=}")
        if not proceed():
            break

Answer 2

除了Razumov建议的调整缩进外，还要注意“输入另一个数字”的那部分代码永远不会执行，因为每次循环开始时，last_answer都会被重置为None。我们只在一开始的时候把它设为None就可以了……

如果你想在循环中报告一个累加的总和，可以试试这个：

class calc:
    @staticmethod
    def addNums(*args):
        return sum(args)


def showAddition():
    print("You have selected: \"Addition\"")

    last_answer = None
    while True:
        if last_answer:
                        next_num = int(input("Please input another number: "))
            answer = calc.addNums(last_answer, next_num)
        else:
            num1 = int(input("Please enter your first number: "))
            num2 = int(input("Please enter your second number: "))
            answer = calc.addNums(num1, num2)

        print(f'Your answer is {answer}')
        continue_prompt = input("Would you like to continue? Y/N\n")

        if continue_prompt.upper() == "Y" or continue_prompt.upper() == "YES":
            last_answer = answer
        else:
            break

（你没有提供calc.addNums的具体实现，我加了一个实现，这样我才能运行代码。）

Answer 3

def showAddition():
    print("You have selected: \"Addition\"")
    
    # store the result of the previous addition
    last_answer = None
    # to stop the loop
    continue_adding = True
    
    while continue_adding:
        if last_answer:
            next_num = int(input("Please input another number: "))
            # answer = last_answer + next_num
            answer = calc.addNums(last_answer, next_num)
            print(f'Your answer is {answer}')
            # store new value in last answer
            last_answer = answer
        else:
            num1 = int(input("Please enter your first number: "))
            num2 = int(input("Please enter your second number: "))
            # answer = num1 + num2 
            answer = calc.addNums(num1, num2)
                
            print(f'Your answer is {answer}')
            
            # check input
            while True:
                continue_prompt = input("Would you like to continue? Y/N\n")
                # continue addition directly with stored last_answer
                if continue_prompt.upper() in {"Y","YES"}:
                    last_answer = answer
                    break
                elif continue_prompt.upper() in {"N","NO"}:
                    # stop the loop
                    continue_adding = False
                    break
                else:
                    # ask again to only input Y/N
                    print("Only Enter Either Y/N")
                    continue

以下是一些编程建议，帮助你更好地理解如何处理循环和条件判断：

1. 把上一个答案存储到循环外面的一个变量里，这样在下次循环时就不会被重置了。
2. 设置一个循环变量叫做 continue_loop，用来控制循环的停止，这样当输入不是 Y 或 N 时，就不用写太多代码来处理。
3. 与其使用 if x == y 这样的比较，不如使用集合或列表来查找，比如 if x in [x,y,z]。