python 中自定义异常的错误处理

Question

我正在尝试对这些运算符设置错误异常。基本上，如果输入的不是列表中的项目，我想抛出一个错误。我知道为什么这段代码不起作用，但我不确定如何修复它。请帮助我完成这项工作。谢谢

while True:
        sign = ["+", "-" , "/" , "*"]
        try:
            operation_type=(input("what operation type you want to do?"))
            for i in range (len(sign)) :
                
                if (operation_type!= sign[i]):
                    print ("pass")
                    raise Invalid
                    i+=1
                break
        except Invalid:
            print("Please input + or - or / or *")

Answer 1

这是我发现效果最好的方法（我已经包含了应该解释一切的评论）：

sign = ["+", "-" , "/" , "*"]

while True:
    operation_type=input("what operation type you want to do?")

    if operation_type in sign:#If the input is in one of the operations in sign, then quit.
        print(operation_type, 'passed')
        break#Break out of checking loop, as the requirement is met

    print('that is not the required operation')#Essentially your exception
         
 print('program done')

希望这就是您要找的！

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