The Fix
pip install requests==2.27.0
Based on closed psf/requests issue #2345 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -36,6 +36,8 @@
from .models import REDIRECT_STATI
+REDIRECT_CACHE_SIZE = 1000
+
Option A — Upgrade to fixed release\npip install requests==2.27.0\nWhen NOT to use: This fix should not be used if the application relies on the original threading behavior of RecentlyUsedContainer.\n\n
Why This Fix Works in Production
- Trigger: Using RecentlyUsedContainer for session cache breaks pickling
- Mechanism: Changes in RecentlyUsedContainer's implementation broke pickling of Session objects
- Why the fix works: Properly serialize RecentlyUsedContainers for cache to handle pickling issues. (first fixed release: 2.27.0).
- 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
- Changes in RecentlyUsedContainer's implementation broke pickling of Session objects
- Production symptom (often without a traceback): Using RecentlyUsedContainer for session cache breaks pickling
Proof / Evidence
- GitHub issue: #2345
- Fix PR: https://github.com/psf/requests/pull/2349
- First fixed release: 2.27.0
- Reproduced locally: No (not executed)
- Last verified: 2026-02-07
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.82
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“So we can't just remove redirect_cache from the list of __attrs__, it breaks the tests”
“Note to @kennethreitz, we **can not** do a release until we fix this.”
“@mattrobenolt Not your fault, our CI was busted so you had no way to know. =)”
“Also, we told you to take this approach. Not your fault in the slightest.”
Failure Signature (Search String)
- Using RecentlyUsedContainer for session cache breaks pickling
- The changes in 387c8f8 have broken the ability to pickle a Session object.
Copy-friendly signature
Failure Signature
-----------------
Using RecentlyUsedContainer for session cache breaks pickling
The changes in 387c8f8 have broken the ability to pickle a Session object.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Using RecentlyUsedContainer for session cache breaks pickling
The changes in 387c8f8 have broken the ability to pickle a Session object.
What Broke
Attempting to pickle a Session object results in errors and prevents proper serialization.
Why It Broke
Changes in RecentlyUsedContainer's implementation broke pickling of Session objects
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install requests==2.27.0
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/psf/requests/pull/2349
First fixed release: 2.27.0
Last verified: 2026-02-07. Validate in your environment.
When NOT to Use This Fix
- This fix should not be used if the application relies on the original threading behavior of RecentlyUsedContainer.
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.
Version Compatibility Table
| Version | Status |
|---|---|
| 2.27.0 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.