Bug: APIGatewayRestResolver exception_handler decorator is not stackable

Expected Behaviour

I would expect to be able to decorate an exception handler multiple times to reuse handler code.

@app.exception_handler(SchemaValidationError)
@app.exception_handler(BadRequestError)
def handle_it(ex):
    pass

Current Behaviour

The first decorator (immediately above the function header) is handled correctly, however subsequent decorators are assigned None in the map and are therefore not handled. In the example above, a SchemaValidationError would result in a 502 Internal Server error response to the user.

Code snippet

from aws_lambda_powertools.event_handler import APIGatewayRestResolver
from aws_lambda_powertools.event_handler.exceptions import BadRequestError
from aws_lambda_powertools.utilities.validation import SchemaValidationError
app = APIGatewayRestResolver()

@app.exception_handler(SchemaValidationError)
@app.exception_handler(BadRequestError)
def something():
    pass

Possible Solution

Return the function in the inner function:

def exception_handler(self, exc_class: Type[Exception]):
        def register_exception_handler(func: Callable):
            self._exception_handlers[exc_class] = func
            return func

        return register_exception_handler

Steps to Reproduce

Add some logging to powertools for illustration:

def exception_handler(self, exc_class: Type[Exception]):
    def register_exception_handler(func: Callable):
        self._exception_handlers[exc_class] = func
        print(self._exception_handlers)

Run the code snippet above. Note the output e.g.

{<class 'aws_lambda_powertools.event_handler.exceptions.BadRequestError'>: <function something at 0x108813310>, <class 'aws_lambda_powertools.utilities.validation.exceptions.SchemaValidationError'>: None}

AWS Lambda Powertools for Python version

37

AWS Lambda function runtime

3.9

Packaging format used

Lambda Layers

Debugging logs

No response

[sprkem]

I have raised this now: https://github.com/awslabs/aws-lambda-powertools-python/pull/1707

[github-actions[bot]]

This is now released under 2.3.0 version!