The Fix
pip install fastapi==0.128.5
Based on closed fastapi/fastapi issue #13150 · PR/commit linked
@@ -1,17 +1,35 @@
@@ -1,17 +1,35 @@
+import importlib
+
+import pytest
Option A — Upgrade to fixed release\npip install fastapi==0.128.5\nWhen NOT to use: This fix should not be used if maintaining separate tests for each variant is necessary for clarity.\n\n
Why This Fix Works in Production
- Trigger: For example, for `docs_src/query_params_str_validations/tutorial010.py`, for this same `tutorial010`, we have these variants:
- Mechanism: Multiple test files for variants led to redundancy and complexity in the test suite
- Why the fix works: Simplified tests for variants by consolidating multiple test files into a single parameterized test file. (first fixed release: 0.128.5).
Why This Breaks in Prod
- Shows up under Python 3.8 in real deployments (not just unit tests).
- Multiple test files for variants led to redundancy and complexity in the test suite
- Production symptom (often without a traceback): For example, for `docs_src/query_params_str_validations/tutorial010.py`, for this same `tutorial010`, we have these variants:
Proof / Evidence
- GitHub issue: #13150
- Fix PR: https://github.com/fastapi/fastapi/pull/13149
- First fixed release: 0.128.5
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.95
- 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).
“@alejsdev: I think I will be able to help”
“I can help , please let me know the tests to be worked on.”
“Hi @alejsdev @tiangolo. May you please take a look at my open PRs above? Thank you :)”
“Seems that this is done for Python version variants (except test_websockets, but we decided not to update it (Python 3.8 support will likely be dropped…”
Failure Signature (Search String)
- For example, for `docs_src/query_params_str_validations/tutorial010.py`, for this same `tutorial010`, we have these variants:
- * `docs_src/query_params_str_validations/tutorial010_an_py39.py`
Copy-friendly signature
Failure Signature
-----------------
For example, for `docs_src/query_params_str_validations/tutorial010.py`, for this same `tutorial010`, we have these variants:
* `docs_src/query_params_str_validations/tutorial010_an_py39.py`
Error Message
Signature-only (no traceback captured)
Error Message
-------------
For example, for `docs_src/query_params_str_validations/tutorial010.py`, for this same `tutorial010`, we have these variants:
* `docs_src/query_params_str_validations/tutorial010_an_py39.py`
Environment
- Python: 3.8
What Broke
Increased maintenance burden and potential for inconsistent test results across variants.
Why It Broke
Multiple test files for variants led to redundancy and complexity in the test suite
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install fastapi==0.128.5
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/fastapi/fastapi/pull/13149
First fixed release: 0.128.5
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be used if maintaining separate tests for each variant is necessary for clarity.
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 |
|---|---|
| 0.128.5 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.