This document describes the current stable version of Celery (4.2). For development docs, go here.

What’s new in Celery 4.2 (windowlicker)

Author:Omer Katz (omer.drow at

Celery is a simple, flexible, and reliable distributed system to process vast amounts of messages, while providing operations with the tools required to maintain such a system.

It’s a task queue with focus on real-time processing, while also supporting task scheduling.

Celery has a large and diverse community of users and contributors, you should come join us on IRC or our mailing-list.

To read more about Celery you should go read the introduction.

While this version is backward compatible with previous versions it’s important that you read the following section.

This version is officially supported on CPython 2.7, 3.4, 3.5 & 3.6 and is also supported on PyPy.

Table of Contents

Make sure you read the important notes before upgrading to this version.


The 4.2.0 release continues to improve our efforts to provide you with the best task execution platform for Python.

This release is mainly a bug fix release, ironing out some issues and regressions found in Celery 4.0.0.

Traditionally, releases were named after Autechre’s track names. This release continues this tradition in a slightly different way. Each major version of Celery will use a different artist’s track names as codenames.

From now on, the 4.x series will be codenamed after Aphex Twin’s track names. This release is codenamed after his very famous track, Windowlicker.

Thank you for your support!

— Omer Katz

Wall of Contributors

Alejandro Varas <> Alex Garel <> Alex Hill <> Alex Zaitsev <> Alexander Ovechkin <> Andrew Wong <> Anton <> Anton Gladkov <> Armenak Baburyan <> Asif Saifuddin Auvi <> BR <> Ben Welsh <> Bohdan Rybak <> Chris Mitchell <> DDevine <> Dan Wilson <> David Baumgold <> David Davis <> Denis Podlesniy <> Denis Shirokov <> Fengyuan Chen <> GDR! <> Geoffrey Bauduin <> George Psarakis <> Harry Moreno <> Huang Huang <> Igor Kasianov <> JJ <> Jackie Leng <> James M. Allen <> Javier Martin Montull <> John Arnold <> Jon Dufresne <> Jozef <> Kevin Gu <> Kxrr <Hi@Kxrr.Us> Leo Singer <> Mads Jensen <> Manuel Vázquez Acosta <> Marcelo Da Cruz Pinto <> Marco Schweighauser <> Markus Kaiserswerth <> Matt Davis <> Michael <> Michael Peake <> Mikołaj <> Misha Wolfson <> Nick Eaket <> Nicolas Mota <> Nicholas Pilon <> Omer Katz <> Patrick Cloke <> Patrick Zhang <> Paulo <> Rachel Johnson <> Raphaël Riel <> Russell Keith-Magee <> Ryan Guest <> Ryan P Kilby <> Régis B <> Sammie S. Taunton <> Samuel Dion-Girardeau <> Scott Cooper <> Sergi Almacellas Abellana <> Sergio Fernandez <> Shitikanth <> Theodore Dubois <> Thijs Triemstra <> Tobias Kunze <> Vincent Barbaresi <> Vinod Chandru <> Wido den Hollander <> Xavier Hardy <> anentropic <> arpanshah29 <> dmollerm <> hclihn <> jess <> lead2gold <> mariia-zelenova <> martialp <> mperice <> pachewise <> partizan <> y0ngdi <>


This wall was automatically generated from git history, so sadly it doesn’t not include the people who help with more important things like answering mailing-list questions.

Important Notes

Supported Python Versions

The supported Python Versions are:

  • CPython 2.7
  • CPython 3.4
  • CPython 3.5
  • CPython 3.6
  • PyPy 5.8 (pypy2)


Result Backends

New Redis Sentinel Results Backend

Redis Sentinel provides high availability for Redis. A new result backend supporting it was added.

Cassandra Results Backend

A new cassandra_options configuration option was introduced in order to configure the cassandra client.

See Cassandra backend settings for more information.

DynamoDB Results Backend

A new dynamodb_endpoint_url configuration option was introduced in order to point the result backend to a local endpoint during development or testing.

See AWS DynamoDB backend settings for more information.

Python 2/3 Compatibility Fixes

Both the CouchDB and the Consul result backends accepted byte strings without decoding them to Unicode first. This is now no longer the case.


Multiple bugs were resolved resulting in a much smoother experience when using Canvas.


Bound Tasks as Error Callbacks

We fixed a regression that occured when bound tasks are used as error callbacks. This used to work in Celery 3.x but raised an exception in 4.x until this release.

In both 4.0 and 4.1 the following code wouldn’t work:

@app.task(name="raise_exception", bind=True)
def raise_exception(self):
    raise Exception("Bad things happened")

@app.task(name="handle_task_exception", bind=True)
def handle_task_exception(self):
    print("Exception detected")

subtask = raise_exception.subtask()


Task Representation

  • Shadowing task names now works as expected. The shadowed name is properly presented in flower, the logs and the traces.
  • argsrepr and kwargsrepr were previously not used even if specified. They now work as expected. See Hiding sensitive information in arguments for more information.

Custom Requests

We now allow tasks to use custom request classes for custom task classes.

See Requests and custom requests for more information.

Retries with Exponential Backoff

Retries can now be performed with exponential backoffs to avoid overwhelming external services with requests.

See Automatic retry for known exceptions for more information.

Sphinx Extension

Tasks were supposed to be automatically documented when using Sphinx’s Autodoc was used. The code that would have allowed automatic documentation had a few bugs which are now fixed.

Also, The extension is now documented properly. See Documenting Tasks with Sphinx for more information.