mirror of https://github.com/pallets/flask.git
78 lines
2.9 KiB
ReStructuredText
78 lines
2.9 KiB
ReStructuredText
Custom Error Pages
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==================
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Flask comes with a handy :func:`~flask.abort` function that aborts a
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request with an HTTP error code early. It will also provide a plain black
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and white error page for you with a basic description, but nothing fancy.
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Depending on the error code it is less or more likely for the user to
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actually see such an error.
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Common Error Codes
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------------------
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The following error codes are some that are often displayed to the user,
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even if the application behaves correctly:
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*404 Not Found*
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The good old "chap, you made a mistake typing that URL" message. So
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common that even novices to the internet know that 404 means: damn,
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the thing I was looking for is not there. It's a very good idea to
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make sure there is actually something useful on a 404 page, at least a
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link back to the index.
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*403 Forbidden*
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If you have some kind of access control on your website, you will have
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to send a 403 code for disallowed resources. So make sure the user
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is not lost when he tries to access a resource he cannot access.
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*410 Gone*
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Did you know that there the "404 Not Found" has a brother named "410
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Gone"? Few people actually implement that, but the idea is that
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resources that previously existed and got deleted answer with 410
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instead of 404. If you are not deleting documents permanently from
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the database but just mark them as deleted, do the user a favour and
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use the 410 code instead and display a message that what he was
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looking for was deleted for all eternity.
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*500 Internal Server Error*
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Usually happens on programming errors or if the server is overloaded.
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A terrible good idea to have a nice page there, because your
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application *will* fail sooner or later (see also:
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:ref:`application-errors`).
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Error Handlers
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--------------
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An error handler is a function, just like a view function, but it is
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called when an error happens and is passed that error. The error is most
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likely a :exc:`~werkzeug.exceptions.HTTPException`, but in one case it
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can be a different error: a handler for internal server errors will be
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passed other exception instances as well if they are uncaught.
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An error handler is registered with the :meth:`~flask.Flask.errorhandler`
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decorator and the error code of the exception. Keep in mind that Flask
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will *not* set the error code for you, so make sure to also provide the
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HTTP status code when returning a response.
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Here an example implementation for a "404 Page Not Found" exception::
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from flask import render_template
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@app.errorhandler(404)
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def page_not_found(e):
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return render_template('404.html'), 404
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An example template might be this:
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.. sourcecode:: html+jinja
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{% extends "layout.html" %}
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{% block title %}Page Not Found{% endblock %}
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{% block body %}
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<h1>Page Not Found</h1>
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<p>What you were looking for is just not there.
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<p><a href="{{ url_for('index') }}">go somewhere nice</a>
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{% endblock %}
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