Pass arguments to flask error handler

Question

On my website, I want to be able to give the user better feedback on a 404 error than "page not found". If a view raises a 404 error, I want to pass an extra parameter to the template that describes what the view shows. For instance:

views.py

def get_or_404(model, attribute, value, template, **kwargs):
    try:
        return session.query(model).filter(attribute == value).one()
    except NoResultFound:
        abort(404)

@app.errorhandler(404)
def page_not_found(error):
    return render_template("404.html"), 404

@app.route("project/<project_id>")
def project_show(project_id):
    """
    Show the files contained in a specific project.

    :param int project_id: The ID of the desired project.
    """

    project = get_or_404(Project, Project.id, project_id, "item_not_found.html", item="project")

    # Other stuff

If the user attempts to go to a project that does not exist, then they are sent to a 404 page. If I can provide the item kwarg (from project_show) to the template 404.html, then the template will say, for instance, "Project not found" instead of just "page not found".

What is the best way to do this?

pigi5 · Accepted Answer · 2018-01-02 08:57:58Z

4

The errorhandler route already has an error argument. When you call abort(), Flask throws an HTTPException, which errorhandler is waiting for. The main idea here is that you can create your own exception hierarchy or one exception with different properties and use it in your errorhandler template.

The second idea is to use flashing: on exception, flash a message and abort(), then in your errorhandler template pick up this message.

edited Jan 2, 2018 at 8:57

pigi5

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answered Apr 23, 2014 at 4:40

tbicr

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2 Comments

Plasma Over a year ago

How can I "create my own exceptions hierarchy?" Won't HTTPException always be thrown when I call abort()?

tbicr Over a year ago

See flask.pocoo.org/docs/api/…, you can catch any exception with errorhandler. So your exception can be look like class ProjectNotFoundException(Exception): pass and catch with @app.errorhandler(ProjectNotFoundException).

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