Can we have Flask error handlers in separate module

Question

We are migrating our Flask app from function based views to pluggable views, all working as expected, except the error handlers. I am trying to put all the error handlers in a s

Answer 1

While you can do this using some circular imports, e.g.:

app.py

import flask

app = flask.Flask(__name__)

import error_handlers

error_handlers.py

from app import app

@app.errorhandler(404)
def handle404(e):
    return '404 handled'

Apparently, this may get tricky in more complex scenarios.

Flask has a clean and flexible way to compose an applications from multiple modules, a concept of blueprints. To register error handlers using a flask.Blueprint you can use either of these:

• flask.Blueprint.errorhandler decorator to handle local blueprint errors

• flask.Blueprint.app_errorhandler decorator to handle global app errors.

Example:

error_handlers.py

import flask

blueprint = flask.Blueprint('error_handlers', __name__)

@blueprint.app_errorhandler(404)
def handle404(e):
    return '404 handled'

app.py

import flask
import error_handlers

app = flask.Flask(__name__)
app.register_blueprint(error_handlers.blueprint)

Both ways achieve the same, depends what suits you better.

Answer 2

@NaturalBornCamper said that he was getting errors. I had to google around a bit but this is what I ended up with for now. I tried to reply to his comment but I did not have enough reputation.

My solution followed the blueprints path and having each blueprint have its own templates and static folder as well.

I have it under src/app/blueprints/errors/handlers.py

from flask import Blueprint

bp = Blueprint('errors',
               __name__,
               template_folder='templates',
               static_folder='static', )

@bp.app_errorhandler(404)
def handle404(error):
    return '404 handled'

With the following in my init at src/app/blueprints/errors/__init__.py:

from .handlers import bp as errors_bp

If you want your blueprint to handle its own errors you would do:

@bp.errorhandler()

But from my understanding this won't catch some errors because blueprints routes are registered differently so it might behave differently then you expect.

This is what I have as the factory application under src/app/__init__.py

from flask import Flask

def create_app():
    from app.blueprints.personal import personal_bp
    from app.blueprints.errors import errors_bp
    app = Flask(__name__, instance_relative_config=True)
    app.register_blueprint(personal_bp, url_prefix='/') # blueprint for my personal site set to the default route
    app.register_blueprint(errors_bp)
    return app

Then I run the following command to test with it flask from /src:

> export FLASK_APP=app
> export FLASK_APP=development
> flask run

Answer 3

I think you import error_handlers module in routing.py as like

import error_handlers

Better you do import like following as in routing.py

from error_handlers import *

It could be help you:-)