Flask – How to create custom abort() code?

Question

Flask has a good error handler by using abort() or when the error truly occurred.

From Flask documentation there is an example for error 404 handler:

@app.errorhandler(404)
def not_found(error):
    return render_template('404.html'), 404

So, I tried to create custom error code like

if False:
    abort(777)

@app.errorhandler(777)
def something_is_wrong(error):
    return render_template('777.html'), 777

But it does not work and the Werkzeug debugger says: LookupError: no exception for 777

I found this question which says I should do it like this:

if False:
    return '777 error', 777

Unfortunately, the code above produce white-screen, even the Werkzeug debugger does not come out

I know I can simply do:

if False:
    return render_template('777.html')

But it will make the code cleaner if I use the abort(). Is there any way to create custom error code?

Asked By: hrsetyono

||

Source

Answer 1

The list of possible HTTP status codes is fixed by the Internet Assigned Numbers Authority, so you cannot add a custom one. Werkzeug recognizes this and tries to stop you sending a meaningless code to the browser. Look through the list of status codes to find one that matches your error and use that one.

Edit: Adding status codes to Werkzeug/Flask

import werkzeug.exceptions as ex
from flask import Flask, abort

class PaymentRequired(ex.HTTPException):
    code = 402
    description = '<p>You will pay for this!</p>'

abort.mappings[402] = PaymentRequired

app = Flask(__name__)

@app.route('/')
def mainpage():
    abort(402)

@app.errorhandler(402)
def payme(e):
    return 'Pay me!'

app.run()

Answered By: Abe Karplus

Answer 2

Depending on the reading of the question this might come in handy.

There is an easier way to add customer error page handling for a specific exception, you can do this:

class MyCustom404(Exception):
    pass

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

@app.errorhandler(MyCustom404)
def special_page_not_found(error):
    return render_template("errors/custom_404.html"), 404

…then trigger your new handler when you need it with

raise MyCustom404

See the docs here.

Answered By: Andrew Barrett

Answer 3

You could also use Flask API and its error handling system:

http://www.flaskapi.org/api-guide/exceptions/

Answered By: Mathieu Rodic

Answer 4

In my case, Flask==0.11.1 Werkzeug==0.11.10

I use abort the http status code 451 for example.

if you want use abort() with a code,a int number,like abort(451), at first you should create a custom HTTPException, a subclass of HTTPException.and append your HTTPException to default_exceptions.

from werkzeug.exceptions import HTTPException, default_exceptions,  Aborter
class UnavailableForLegalReasons(HTTPException):
    code = 451
    description = 'BIG BROTHER IS WATCHING YOU'

default_exceptions[451] = UnavailableForLegalReasons
abort = Aborter()  # don't from flask import abort

@app.errorhandler(451)
def uflr(e):
    return e, 451

@app.route('/debug')
def debug():
    abort(451)

then when you access the path in browser, you can look this

but the http reason phrase is UNKNOWN,

you can change it

from werkzeug.http import HTTP_STATUS_CODES
HTTP_STATUS_CODES[451] = 'Unavailable For Legal Reasons'  # or even empty

Answered By: xavierskip

Flask – How to create custom abort() code?

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