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Reputation: 4894

flask: error_handler for blueprints

Can error_handler be set for a blueprint?

@blueprint.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

edit:

https://github.com/mitsuhiko/flask/blob/18413ed1bf08261acf6d40f8ba65a98ae586bb29/flask/blueprints.py

you can specify an app wide and a blueprint local error_handler

Upvotes: 45

Views: 24210

Answers (7)

godzillante
godzillante

Reputation: 1214

I combined previous excellent answers with the official docs from Flask, section 'Returning API Errors as JSON', in order to provide a more general approach.

Here is a working PoC that you can copy and paste on your registered blueprint API route handler (e.g. app/api/routes.py):

    from werkzeug.exceptions import HTTPException

    @blueprint.app_errorhandler(HTTPException)
    def handle_exception(e):
        """Return JSON instead of HTML for HTTP errors."""
        # start with the correct headers and status code from the error
        response = e.get_response()
        # replace the body with JSON
        response.data = json.dumps({
            "code": e.code,
            "name": e.name,
            "description": e.description,
        })
        response.content_type = "application/json"
        return response

Upvotes: 2

CodingMatters
CodingMatters

Reputation: 1431

Surprised others didn't mention miguelgrinberg's excellent tutorial.

https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-vii-error-handling

I found the sentry framework for error handling (links below). Seems overly complex. not sure of the threshold where it becomes useful.

https://flask.palletsprojects.com/en/1.1.x/errorhandling/

https://docs.sentry.io/platforms/python/guides/flask/

Upvotes: 1

TjerkW
TjerkW

Reputation: 2150

Flask doesnt support blueprint level error handlers for 404 and 500 errors. A BluePrint is a leaky abstraction. Its better to use a new WSGI App for this, if you need separate error handlers, this makes more sense.

Also i would recommend not to use flask, it uses globals all over the places, which makes your code difficult to manage if it grows bigger.

Upvotes: -10

T. Goncalves
T. Goncalves

Reputation: 351

errorhandler is a method inherited from Flask, not Blueprint. If you are using Blueprint, the equivalent is app_errorhandler.

The documentation suggests the following approach:

def app_errorhandler(self, code):
        """Like :meth:`Flask.errorhandler` but for a blueprint.  This
        handler is used for all requests, even if outside of the blueprint.
        """

Therefore, this should work:

from flask import Blueprint, render_template

USER = Blueprint('user', __name__)

@USER.app_errorhandler(404)
def page_not_found(e):
    """ Return error 404 """
    return render_template('404.html'), 404

On the other hand, while the approach below did not raise any error for me, it didn't work:

from flask import Blueprint, render_template

USER = Blueprint('user', __name__)

@USER.errorhandler(404)
def page_not_found(e):
    """ Return error 404 """
    return render_template('404.html'), 404

Upvotes: 24

swarup260
swarup260

Reputation: 126

add error handling at application level using the request proxy object:

from flask import request,jsonify

@app.errorhandler(404)
@app.errorhandler(405)
def _handle_api_error(ex):
if request.path.startswith('/api/'):
    return jsonify(ex)
else:
    return ex

flask Documentation

Upvotes: 3

Jonathan Deakin
Jonathan Deakin

Reputation: 100

I too couldn't get the top rated answer to work, but here's a workaround.

You can use a catch-all at the end of your Blueprint, not sure how robust/recommended it is, but it does work. You could also add different error messages for different methods too.

@blueprint.route('/<path:path>')
def page_not_found(path):
    return "Custom failure message"

Upvotes: 2

suzanshakya
suzanshakya

Reputation: 3650

You can use Blueprint.app_errorhandler method like this:

bp = Blueprint('errors', __name__)

@bp.app_errorhandler(404)
def handle_404(err):
    return render_template('404.html'), 404

@bp.app_errorhandler(500)
def handle_500(err):
    return render_template('500.html'), 500

Upvotes: 50

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