Celery Deprecate iso8601 module (Fix)

The Fix

Deprecates the iso8601 module in favor of using datetime.datetime.fromisoformat().

Based on closed celery/celery issue #8080 · 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.

Open PR/Commit

@@ -14,7 +14,6 @@
 from .exceptions import ImproperlyConfigured, IncompleteStream, TimeoutError
 from .utils.graph import DependencyGraph, GraphFormatter
-from .utils.iso8601 import parse_iso8601
 
 try:

fix.md

Option A — Apply the official fix\nDeprecates the iso8601 module in favor of using datetime.datetime.fromisoformat().\nWhen NOT to use: Do not use this fix if your application must support versions of Python older than 3.7.\n\n

Why This Fix Works in Production

Trigger: - [x] I have included all related issues and possible duplicate issues in this issue
Mechanism: Deprecates the iso8601 module in favor of using datetime.datetime.fromisoformat().

Production impact:

If left unfixed, retries/timeouts can trigger duplicate external side-effects (double charges, duplicate emails, repeated writes).

Why This Breaks in Prod

Shows up under Python 3.7 in real deployments (not just unit tests).
Production symptom (often without a traceback): - [x] I have included all related issues and possible duplicate issues in this issue

Proof / Evidence

GitHub issue: #8080
Fix PR: https://github.com/celery/celery/pull/8098
Reproduced locally: No (not executed)
Last verified: 2026-02-11
Confidence: 0.70
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.72

Discussion

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

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“Hey @wongcht :wave:, Thank you for opening an issue”

@open-collective-bot · 2023-02-20 · source

Failure Signature (Search String)

- [x] I have included all related issues and possible duplicate issues in this issue
or possible duplicates to this issue as requested by the checklist above.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
- [x] I have included all related issues and possible duplicate issues in this issue
or possible duplicates to this issue as requested by the checklist above.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
- [x] I have included all related issues and possible duplicate issues in this issue
or possible duplicates to this issue as requested by the checklist above.

Environment

Python: 3.7

What Broke

No immediate production failures, but reliance on deprecated functionality could lead to future issues.

Fix Options (Details)

Option A — Apply the official fix

Deprecates the iso8601 module in favor of using datetime.datetime.fromisoformat().

When NOT to use: Do not use this fix if your application must support versions of Python older than 3.7.

Fix reference: https://github.com/celery/celery/pull/8098

Last verified: 2026-02-11. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if your application must support versions of Python older than 3.7.

Did This Fix Work in Your Case?

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

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Related Issues

No related fixes found.

Cluster: celery:duplicates Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Data consistency Duplicate processing

Sources

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