What is the standard way to design exception inheritance?

user_4283399 0
Viewed 42

Im having some trouble with designing the exception classes for a Python web API. What I would like to do is have various exceptions set up with some default error codes/messages, but also allow the flexibility of creating a custom one.

Take the following code:

class APIException(Exception):
    def __init__(self):
        super().__init__(self.message)

    @property
    def message(self) -> str:
        raise NotImplementedError

    @property
    def code(self) -> int:
        raise NotImplementedError

    @property
    def response(self):
        return {"error": self.message}, self.code


class UnknownException(APIException):
    message = "An unknown error occurred."
    code = 500


class UnauthorizedException(APIException):
    message = "Unauthorized"
    code = 401

This allows me to do things like raise UnauthorizedException, which work fine. However, what I would like to be able to do is to raise arbitrary API exceptions, like raise APIException("This is a custom error", 404). Raising a set exception with arguments and raising an APIException without arguments do not need to be supported; I will not be raising them like that.

It doesn't seem I can do this cleanly with the way I have designed the inheritance above. I have tried other various approaches but none seem to be as clean as the example above.

What would be the best way to go about doing this sort of thing?

python-3.x inheritance oop python
1 Answers

Have your APIException constructor take arguments, and have the subclasses implement constructors that provide those arguments:

class APIException(Exception):
    def __init__(self, message, code):
        super().__init__(message)
        self.message = message
        self.code = code

    @property
    def response(self):
        return {"error": self.message}, self.code


class UnknownException(APIException):
    def __init__():
        super().__init__("An unknown error occurred.", 500)


class UnauthorizedException(APIException):
    def __init__():
        super().__init__("Unauthorized", 401)
user_23571120
Related