Pydantic Documentation error: Incorrect example in

The Fix

pip install pydantic==2.11.4

Based on closed pydantic/pydantic issue #11765 · 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%.

Jump to Verify Open PR/Commit

@@ -194,7 +194,7 @@ class Model(BaseModel):
         #> my_field='foo'
 
-        m = Model(my_alias='foo')  # (3)!
+        m = Model(my_field='foo')  # (3)!
         print(m)

repro.py

pydantic version: 2.11.3
        pydantic-core version: 2.33.1
          pydantic-core build: profile=release pgo=false
                 install path: /home/vscode/.cache/pyuv/.venv/lib/python3.13/site-packages/pydantic
               python version: 3.13.3 (main, Apr  9 2025, 04:03:52) [Clang 20.1.0 ]
                     platform: Linux-6.8.0-57-generic-x86_64-with-glibc2.36
             related packages: pydantic-extra-types-2.10.3 fastapi-0.115.12 pydantic-settings-2.8.1 mypy-1.15.0 typing_extensions-4.13.2
                       commit: unknown

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 pydantic==2.11.4\nWhen NOT to use: This fix should not be used if the documentation is already correct.\n\n

Why This Fix Works in Production

Trigger: Documentation error: Incorrect example in `populate_by_name` docstring
Mechanism: The documentation example for `populate_by_name` incorrectly repeated the previous example instead of showing the correct field
Why the fix works: Fixes the example in the `populate_by_name` documentation, correcting the third example to use `my_field` instead of `my_alias`. (first fixed release: 2.11.4).

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 3.13 in real deployments (not just unit tests).
The documentation example for `populate_by_name` incorrectly repeated the previous example instead of showing the correct field
Production symptom (often without a traceback): Documentation error: Incorrect example in `populate_by_name` docstring

Proof / Evidence

GitHub issue: #11765
Fix PR: https://github.com/pydantic/pydantic/pull/11766
First fixed release: 2.11.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.61

Discussion

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

Jump to Sources Open on GitHub

“### Initial Checks - [x] I confirm that I'm using Pydantic V2 ### Description In the docstring for the populate_by_name configuration setting in pydantic/config.py (lines 168-205), there is an error in the code example that demonstrates the”

Issue thread · issue description · source

Failure Signature (Search String)

Documentation error: Incorrect example in `populate_by_name` docstring

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Documentation error: Incorrect example in `populate_by_name` docstring

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Documentation error: Incorrect example in `populate_by_name` docstring

Minimal Reproduction

repro.py

pydantic version: 2.11.3
        pydantic-core version: 2.33.1
          pydantic-core build: profile=release pgo=false
                 install path: /home/vscode/.cache/pyuv/.venv/lib/python3.13/site-packages/pydantic
               python version: 3.13.3 (main, Apr  9 2025, 04:03:52) [Clang 20.1.0 ]
                     platform: Linux-6.8.0-57-generic-x86_64-with-glibc2.36
             related packages: pydantic-extra-types-2.10.3 fastapi-0.115.12 pydantic-settings-2.8.1 mypy-1.15.0 typing_extensions-4.13.2
                       commit: unknown

Environment

Python: 3.13
Pydantic: 2

What Broke

Users were misled by incorrect documentation, potentially causing confusion in implementation.

Why It Broke

The documentation example for `populate_by_name` incorrectly repeated the previous example instead of showing the correct field

Fix Options (Details)

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

pip install pydantic==2.11.4

When NOT to use: This fix should not be used if the documentation is already correct.

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

Fix reference: https://github.com/pydantic/pydantic/pull/11766

First fixed release: 2.11.4

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

When NOT to Use This Fix

This fix should not be used if the documentation is already correct.

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

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
2.11.4	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:configuration-error Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Data consistency OpenAPI schema Serialization

Sources

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

Pydantic Documentation error: Incorrect example in `populate_by_name` docstring (Fix)