Access @App decorator in Flask using Factory Pattern

Question

How do you access the app object using the factory pattern for decorators? I'm aware that current_app exists, but I can't use that for decorators.

Before using the factory pattern (eg. wrapping App initialization and blueprint registration in a function) I could just do something like:

@app.errorhandler(500)
@app.errorhandler(502)
def generic_errror_handler(error):
    # Some logic here
    return render_template('error.html', error=errror)

But after using the factory pattern I don't see how to achieve this in a good way. Do you initialize them inside the create_app() function?

def create_app():
    app = Flask(__name__)
    initialize_extensions(app)
    register_blueprints(app)
    return app

Answer 1

You can initialize the handlers within the create_app definition, e.g.

def create_app():
    app = Flask(__name__)
    initialize_extensions(app)
    register_blueprints(app)

    @app.errorhandler(500)
    @app.errorhandler(502)
    def generic_errror_handler(error):
        # Some logic here
        return render_template('error.html', error=errror)

    return app

Or, create a separate Python file, say error_handlers.py (example taken from Quokka CMS):

def register_handlers(app):
    if app.config.get('DEBUG') is True:
        app.logger.debug('Skipping error handlers in Debug mode')
        return

    @app.errorhandler(403)
    def forbidden_page(*args, **kwargs):
        # do stuff
        return render_template("errors/access_forbidden.html"), 403

    @app.errorhandler(404)
    def page_not_found(*args, **kwargs):
        # do stuff
        return render_template("errors/page_not_found.html"), 404

    @app.errorhandler(405)
    def method_not_allowed_page(*args, **kwargs):
        # do stuff
        return render_template("errors/method_not_allowed.html"), 405

    @app.errorhandler(500)
    def server_error_page(*args, **kwargs):
        # do stuff
        return render_template("errors/server_error.html"), 500

and call register_handlers from within create_app:

def create_app():
    app = Flask(__name__)
    initialize_extensions(app)
    register_blueprints(app)

    register_handlers(app)

    return app