Celery "Next Steps" error propagation example does not

The Fix

pip install celery==4.4.1

Based on closed celery/celery issue #5964 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -328,26 +328,33 @@ exception, in fact ``result.get()`` will propagate any errors by default:
 .. code-block:: pycon
 
-    >>> res = add.delay(2)
+    >>> res = add.delay(2, '2')
     >>> res.get(timeout=1)

repro.py

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 425, in delay
    return self.apply_async(args, kwargs)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 530, in apply_async
    check_arguments(*(args or ()), **(kwargs or {}))
TypeError: add() missing 1 required positional argument: 'y'

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install celery==4.4.1\nWhen NOT to use: This fix is not applicable if the task signature or arguments are fundamentally changed.\n\n

Why This Fix Works in Production

Trigger: return self.apply_async(args, kwargs)
Mechanism: The documentation example for error propagation does not match the current behavior of the add function
Why the fix works: Fixes the error propagation example in the documentation to match the current behavior by changing the example to use two arguments. (first fixed release: 4.4.1).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.8 in real deployments (not just unit tests).
The documentation example for error propagation does not match the current behavior of the add function
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #5964
Fix PR: https://github.com/celery/celery/pull/5966
First fixed release: 4.4.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.34

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“ # Checklist  - [x] I hav”

Issue thread · issue description · source

Failure Signature (Search String)

return self.apply_async(args, kwargs)

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 425, in delay
    return self.apply_async(args, kwargs)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 530, in apply_async
    check_arguments(*(args or ()), **(kwargs or {}))
TypeError: add() missing 1 required positional argument: 'y'

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/result.py", line 221, in get
    return self.backend.wait_for_pending(
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/backends/asynchronous.py", line 195, in wait_for_pending
    return result.maybe_throw(callback=callback, propagate=propagate)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/result.py", line 333, in maybe_throw
    self.throw(value, self._to_remote_traceback(tb))
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/result.py", line 326, in throw
    self.on_ready.throw(*args, **kwargs)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/vine/promises.py", line 244, in throw
    reraise(type(exc), exc, tb)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/vine/five.py", line 195, in reraise
    raise value
TypeError: unsupported operand type(s) for +: 'int' and 'str'

Minimal Reproduction

repro.py

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 425, in delay
    return self.apply_async(args, kwargs)
  File "/home/abd/python/celery/env/lib/python3.8/site-packages/celery/app/task.py", line 530, in apply_async
    check_arguments(*(args or ()), **(kwargs or {}))
TypeError: add() missing 1 required positional argument: 'y'

Environment

Python: 3.8

Why It Broke

The documentation example for error propagation does not match the current behavior of the add function

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==4.4.1

When NOT to use: This fix is not applicable if the task signature or arguments are fundamentally changed.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/5966

First fixed release: 4.4.1

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix is not applicable if the task signature or arguments are fundamentally changed.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.

Version Compatibility Table

Version	Status
4.4.1	Fixed

Related Issues

No related fixes found.

Cluster: celery:configuration-error Celery hub Celery best practices All hubs All clusters

Related clusters: Data consistency Duplicates Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery "Next Steps" error propagation example does not match the current behavior. (Fix)