app.exception_handler does not work when used in separate file

[arunbhati]

Hi,

I am using APIGatewayRestResolver and I'm having trouble working with @app.exception_handler. When I have APIGatewayRestResolver object and @app.exception_handler decorator in same file then it works but if I create a separate file for exceptions(exceptions.py) and do the import of APIGatewayRestResolver then it doesn't work.
Following are steps to reproduce.

1. Create a lambda function in Python with Lambda Layer for AWS Powertools from here.
2. Attach this Zip file to lambda function - Zip file: Archive.zip
3. Use following input for Lambda request

{
  "resource": "/proxy",
  "path": "/proxy",
  "httpMethod": "GET",
  "headers": null
}

4. Lambda function should fail with following error

{
  "errorMessage": "",
  "errorType": "ValueError",
  "requestId": "24f06853-16fc-4657-9360-40409f0726be",
  "stackTrace": [
    "  File \"/var/task/lambda_function.py\", line 10, in lambda_handler\n    return axis_controllers.main(event, context)\n",
    "  File \"/var/task/src/abc/axis_controllers.py\", line 11, in main\n    return app.resolve(event, context)\n",
    "  File \"/opt/python/aws_lambda_powertools/event_handler/api_gateway.py\", line 498, in resolve\n    return self._resolve().build(self.current_event, self._cors)\n",

5. Now move ValueError exception method from exceptions.py into init.py file in same folder.
6. Rerun test with same input and now lambda output will show expected result(shown below).

{
  "statusCode": 400,
  "headers": {
    "Content-Type": "text/plain"
  },
  "body": "Invalid request",
  "isBase64Encoded": false
}

I don't have much expertise on how decorator works so any help here would be appreciated.
Thanks.

[michaelbrewer]

@arunbhati in your example nothing is referencing exceptions.py so it would not call either of the @app.exception_handler or @app.not_found decorators.

You can verify that exceptions.py is not being referenced by adding a print statement.

So maybe either reference the exceptions.py as an import elsewhere or load it via __init__.py, or move the logic in __init__.py__