Falcon error handling examples

error_handling.py

import falcon
import falcon.routing


class FloatConverter(falcon.routing.BaseConverter):
    def convert(self, value):
        try:
            return float(value)
        except ValueError:
            return None


def serialize_error(req, resp, exception):
    preferred = req.client_prefers((falcon.MEDIA_JSON,))
    if preferred == falcon.MEDIA_JSON:
        resp.content_type = preferred
        resp.data = exception.to_json()
    else:
        report = ['[Custom error serializer]\n']
        for key, value in sorted(exception.to_dict().items()):
            report.append(f'{key}: {value}\n')

        resp.content_type = falcon.MEDIA_TEXT
        resp.text = ''.join(report)

    resp.append_header('Vary', 'Accept')


def handle_overflow(req, resp, ex, params):
    if 'power' in params and params['power'] >= 1000:
        # Reraise an instance of HTTPError
        raise falcon.HTTPBadRequest(title='Too Damn High!')

    # Render a custom error response
    resp.content_type = falcon.MEDIA_TEXT
    resp.text = 'That was too much to handle... Check your parameters.\n'
    resp.status = falcon.HTTP_UNPROCESSABLE_ENTITY


class Division:
    def on_get(self, req, resp, dividend, divisor):
        # Divide by 0 to make Falcon return a generic 500 response
        resp.media = dividend / divisor


class Exponentiation:
    def on_get(self, req, resp, base, power):
        resp.media = base ** power


app = falcon.App()
app.router_options.converters['float'] = FloatConverter

app.add_error_handler(OverflowError, handle_overflow)
app.set_error_serializer(serialize_error)

app.add_route('/division/{dividend:float}/{divisor:float}', Division())
app.add_route('/exponentiation/{base:float}^{power:float}', Exponentiation())

does this make sense to have this in the example folder?

Probably it does, but it needs to be cleaned up a bit. I'll drop a link on the respective GH issue: falconry/falcon#1460.