Why is my Flask error handler not being called?

Referring to both this question, and the docs, the key piece of information I took from both is if your route is a Flask-RESTful one, which yours is, it will be handled by handle_error(), and the only way to prevent or customise this is to implement your own API class, and override handle_error().

Following up on @dylanj.nz's answer, this vanilla-Flask error handling method, and this example of overriding Flask-RESTful's API , here's the method I settled on. It allows Flask-RESTful to handle HTTPException types of exceptions, but passes everything else through to the default (Flask) handler, where custom error messages can be specified (an entire JSON object of key/value entries, if you want) at the time of the exception.

from flask_restful import Resource, Api as _Api, HTTPExceptionapp = Flask(__name__)# This new Exception will accept a message, a status code, and a# payload of other values to be displayed as a JSON objectclass FlaskGenericException(Exception):    status_code = 500   # default unless overridden    def __init__(self, message, status_code=None, payload=None):        Exception.__init__(self)        self.message = message        if status_code is not None:            self.status_code = status_code        self.payload = payload    def to_dict(self):        rv = dict(self.payload or ())        rv['message'] = self.message        return rv@app.errorhandler(FlaskGenericException)def handle_flask_generic_error(error):    response = jsonify(error.to_dict())    response.status_code = error.status_code    return response# This overridden Flask-RESTful API class will keep Flask-RESTful# from handling errors other than HTTPException ones.class Api(_Api):    def error_router(self, original_handler, e):        # Override original error_router to only handle HTTPExceptions.        if self._has_fr_route() and isinstance(e, HTTPException):            try:                # Use Flask-RESTful's error handling method                return self.handle_error(e)             except Exception:                # Fall through to original handler (i.e. Flask)                pass        return original_handler(e)api = Api(app)class TestMe(Resource):    def get(self):        try:            ldapc = ldap.connection        except:            # message = first parameter.  Other parameters come in as "payload"            raise FlaskGenericException('A generic error', status_code=505, payload={'user': 'John Doe', 'company': 'Foobar Corp.'})api.add_resource(TestMe, '/testme', endpoint='TestMe')