Pydantic Docs examples can't be run (Fix)

The Fix

pip install pydantic==2.12.0

Based on closed pydantic/pydantic issue #9012 · 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

@@ -36,6 +36,7 @@ run_mypy_on_file.py
 # Documentation files
 /docs/changelog.md
+/docs/*.whl
 /docs/theme/mkdocs_run_deps.html
 /site/

repro.py

# /// script
# dependencies = ["logfire", "pydantic_ai_slim[openai]"]
# ///

# This example demonstrates Pydantic AI running with OpenAI!

from pydantic_ai import Agent
import logfire

# configure logfire
logfire.configure(token='__YOUR_LOGFIRE_WRITE_TOKEN__')
logfire.instrument_pydantic_ai()

agent = Agent('openai:gpt-4o')

result = await agent.run(
    'How does pyodide let you run Python in the browser? (short answer please)'
)

print(f'output: {result.output}')

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==2.12.0\nWhen NOT to use: This fix should not be used if the documentation examples are not intended for production use.\n\n

Why This Fix Works in Production

Trigger: Error starting Python: PythonError: Traceback (most recent call last):
Mechanism: The documentation plugin fails to detect the latest version of pydantic due to missing wheel builds
Why the fix works: Fixes the documentation plugin for running code examples in the dev branch, addressing issues with wheel builds for pydantic. (first fixed release: 2.12.0).

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 3.11 in real deployments (not just unit tests).
The documentation plugin fails to detect the latest version of pydantic due to missing wheel builds
Surfaces as: Error starting Python: PythonError: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #9012
Fix PR: https://github.com/pydantic/pydantic/pull/12322
First fixed release: 2.12.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.35

Discussion

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

Jump to Sources Open on GitHub

“Yes @Viicos I was referring to pydantic.run but I checked it again and it works us you said”

@tselepakis · 2025-10-04 · source

“I took a brief look at this”

@sydney-runkle · 2024-03-17 · source

“Probably this is not totally related but I had a similar issue when I was trying the examples of logfire”

@tselepakis · 2025-09-26 · source

“Hi, I've read through the issue and the analysis by @sydney-runkle. As this is still open and unassigned, I'd like to try and tackle it.…”

@JonathanWindell · 2025-10-04 · source

Failure Signature (Search String)

Error starting Python: PythonError: Traceback (most recent call last):

Error Message

Stack trace

error.txt

Error Message
-------------
Error starting Python: PythonError: Traceback (most recent call last):
  File "/lib/python3.11/site-packages/micropip/_micropip.py", line 576, in install
    await transaction.gather_requirements(requirements)
  File "/lib/python3.11/site-packages/micropip/_micropip.py", line 342, in gather_requirements
    await gather(*requirement_promises)
  File "/lib/python3.11/site-packages/micropip/_micropip.py", line 349, in add_requirement
    return await self.add_requirement_inner(Requirement(req))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/lib/python3.11/site-packages/micropip/_micropip.py", line 444, in add_requirement_inner
    wheel = find_wheel(metadata, req)
            ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/lib/python3.11/site-packages/micropip/_micropip.py", line 312, in find_wheel
    raise ValueError(
ValueError: Can't find a pure Python 3 wheel for 'pydantic==2.7.0a1'.
See: https://pyodide.org/en/stable/usage/faq.html#micropip-can-t-find-a-pure-python-wheel
You can use `micropip.install(..., keep_going=True)`to get a list of all packages with missing wheels.

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/tmp/pydantic_run/_prepare_env.py", line 104, in prepare_env
    await micropip.install(install_dependencies, keep_going=True)
  File "/lib/python3.12/site-packages/micropip/package_manager.py", line 146, in install
    return await install(
           ^^^^^^^^^^^^^^
  File "/lib/python3.12/site-packages/micropip/install.py", line 56, in install
    raise ValueError(
ValueError: Can't find a pure Python 3 wheel for: 'pydantic-core==2.33.2'
See: https://pyodide.org/en/stable/usage/faq.html#why-can-t-micropip-find-a-pure-python-wheel-for-a-package

Minimal Reproduction

repro.py

# /// script
# dependencies = ["logfire", "pydantic_ai_slim[openai]"]
# ///

# This example demonstrates Pydantic AI running with OpenAI!

from pydantic_ai import Agent
import logfire

# configure logfire
logfire.configure(token='__YOUR_LOGFIRE_WRITE_TOKEN__')
logfire.instrument_pydantic_ai()

agent = Agent('openai:gpt-4o')

result = await agent.run(
    'How does pyodide let you run Python in the browser? (short answer please)'
)

print(f'output: {result.output}')

Environment

Python: 3.11

What Broke

Users cannot run documentation examples, leading to confusion and potential loss of trust in the library.

Why It Broke

The documentation plugin fails to detect the latest version of pydantic due to missing wheel builds

Fix Options (Details)

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

pip install pydantic==2.12.0

When NOT to use: This fix should not be used if the documentation examples are not intended for production use.

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/12322

First fixed release: 2.12.0

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

When NOT to Use This Fix

This fix should not be used if the documentation examples are not intended for production use.

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
2.12.0	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.