Flask-restful - Custom error handling

Question

I want to define custom error handling for a Flask-restful API.

The suggested approach in the documentation here is to do the following:

errors = {
    'UserAlreadyExistsError': {
        'message': "A user with that username already exists.",
        'status': 409,
    },
    'ResourceDoesNotExist': {
        'message': "A resource with that ID no longer exists.",
        'status': 410,
        'extra': "Any extra information you want.",
    },
}
app = Flask(__name__)
api = flask_restful.Api(app, errors=errors)

Now I find this format pretty attractive but I need to specify more parameters when some exception happens. For example, when encountering ResourceDoesNotExist, I want to specify what id does not exist.

Currently, I'm doing the following:

app = Flask(__name__)
api = flask_restful.Api(app)


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

    @property
    def code(self):
        return self._code

    @property
    def message(self):
        return self._message

    def __str__(self):
        return self.__class__.__name__ + ': ' + self.message


class ResourceDoesNotExist(APIException):
    """Custom exception when resource is not found."""
    def __init__(self, model_name, id):
        message = 'Resource {} {} not found'.format(model_name.title(), id)
        super(ResourceNotFound, self).__init__(404, message)


class MyResource(Resource):
    def get(self, id):
        try:
            model = MyModel.get(id)
            if not model:
               raise ResourceNotFound(MyModel.__name__, id)
        except APIException as e:
            abort(e.code, str(e))

When called with an id that doesn't exist MyResource will return the following JSON:

{'message': 'ResourceDoesNotExist: Resource MyModel 5 not found'}

This works fine but I'd like to use to Flask-restful error handling instead.

Answer 1

According to the docs

Flask-RESTful will call the handle_error() function on any 400 or 500 error that happens on a Flask-RESTful route, and leave other routes alone.

You can leverage this to implement the required functionality. The only downside is having to create a custom Api.

class CustomApi(flask_restful.Api):

    def handle_error(self, e):
        flask_restful.abort(e.code, str(e))

If you keep your defined exceptions, when an exception occurs, you'll get the same behaviour as

class MyResource(Resource):
    def get(self, id):
        try:
            model = MyModel.get(id)
            if not model:
               raise ResourceNotFound(MyModel.__name__, id)
        except APIException as e:
            abort(e.code, str(e))