Pydantic Class properties have a potential for namespace

The Fix

pip install pydantic==1.10.14

Based on closed pydantic/pydantic issue #9385 · 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.

Jump to Verify Open PR/Commit

@@ -1018,5 +1018,32 @@ except PydanticUserError as exc_info:
 ```
 
+## Cannot evaluate type annotation {#unevaluable-type-annotation}
+
+Because type annotations are evaluated *after* assignments, you might get unexpected results when using a type annotation name

repro.py

from pydantic import BaseModel
from typing import List, Optional

class RulesSource(BaseModel):
    StatelessRulesAndCustomActions: Optional["StatelessRulesAndCustomActions"] = None

class StatelessRulesAndCustomActions(BaseModel):
    StatelessRules: Optional[List["StatelessRule"]] = None

class StatelessRule(BaseModel):
    pass

def test_the_bug():
  # Create instances of the classes to trigger type checking
  rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))

============================================================================================= FAILURES =============================================================================================
___________________________________________________________________________________________ test_the_bug ___________________________________________________________________________________________

    def test_the_bug():
      # Create instances of the classes to trigger type checking
    rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))
E     pydantic_core._pydantic_core.ValidationError: 1 validation error for RulesSource
E     StatelessRulesAndCustomActions
E       Input should be None [type=none_required, input_value=StatelessRulesAndCustomAc...Rules=[StatelessRule()]), input_type=StatelessRulesAndCustomActions]
E         For further information visit https://errors.pydantic.dev/2.7/v/none_required

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==1.10.14\nWhen NOT to use: This fix should not be applied if the model structure is intentionally designed to allow such collisions.\n\n

Why This Fix Works in Production

Trigger: from pydantic import BaseModel
Mechanism: Namespace collision occurs when a class property shares a name with another class and is defined as Optional
Why the fix works: Explicitly raises an error if field names clash with types, addressing potential namespace collisions in Pydantic models. (first fixed release: 1.10.14).

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 3.12 in real deployments (not just unit tests).
Namespace collision occurs when a class property shares a name with another class and is defined as Optional
Surfaces as: from pydantic import BaseModel

Proof / Evidence

GitHub issue: #9385
Fix PR: https://github.com/pydantic/pydantic/pull/8243
First fixed release: 1.10.14
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.28

Discussion

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

Jump to Sources Open on GitHub

“Closing as a duplicate, based on the issues that @Viicos mentioned above. Thanks!”

@sydney-runkle · 2024-05-16 · confirmation · source

“Not sure, might need to double check, but I think this comes from what I described here: https://github.com/pydantic/pydantic/pull/8243#issuecomment-1831900199”

@Viicos · 2024-05-16 · source

“Since Optional[...] is shorthand for Union[..., None] I think that it does. On this same train, now that Union types are a thing in Py3.12,…”

@jrkarnes · 2024-05-16 · source

“This seems to be the same issue as: https://github.com/pydantic/pydantic/issues/7327, https://github.com/pydantic/pydantic/issues/8240, https://github.com/pydantic/pydantic/issues/7309 (see https://github.com/pydantic/pydantic/issues/6646#issuecomment-16339703”

@Viicos · 2024-05-03 · source

Failure Signature (Search String)

from pydantic import BaseModel

Error Message

Stack trace

error.txt

Error Message
-------------
from pydantic import BaseModel
from typing import List, Optional

class RulesSource(BaseModel):
    StatelessRulesAndCustomActions: Optional["StatelessRulesAndCustomActions"] = None

class StatelessRulesAndCustomActions(BaseModel):
    StatelessRules: Optional[List["StatelessRule"]] = None

class StatelessRule(BaseModel):
    pass

def test_the_bug():
  # Create instances of the classes to trigger type checking
  rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))

============================================================================================= FAILURES =============================================================================================
___________________________________________________________________________________________ test_the_bug ___________________________________________________________________________________________

    def test_the_bug():
      # Create instances of the classes to trigger type checking
    rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))
E     pydantic_core._pydantic_core.ValidationError: 1 validation error for RulesSource
E     StatelessRulesAndCustomActions
E       Input should be None [type=none_required, input_value=StatelessRulesAndCustomAc...Rules=[StatelessRule()]), input_
... (truncated) ...

Minimal Reproduction

repro.py

from pydantic import BaseModel
from typing import List, Optional

class RulesSource(BaseModel):
    StatelessRulesAndCustomActions: Optional["StatelessRulesAndCustomActions"] = None

class StatelessRulesAndCustomActions(BaseModel):
    StatelessRules: Optional[List["StatelessRule"]] = None

class StatelessRule(BaseModel):
    pass

def test_the_bug():
  # Create instances of the classes to trigger type checking
  rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))

============================================================================================= FAILURES =============================================================================================
___________________________________________________________________________________________ test_the_bug ___________________________________________________________________________________________

    def test_the_bug():
      # Create instances of the classes to trigger type checking
    rules_source = RulesSource(StatelessRulesAndCustomActions=StatelessRulesAndCustomActions(StatelessRules=[StatelessRule()]))
E     pydantic_core._pydantic_core.ValidationError: 1 validation error for RulesSource
E     StatelessRulesAndCustomActions
E       Input should be None [type=none_required, input_value=StatelessRulesAndCustomAc...Rules=[StatelessRule()]), input_type=StatelessRulesAndCustomActions]
E         For further information visit https://errors.pydantic.dev/2.7/v/none_required

Environment

Python: 3.12
Pydantic: 2

What Broke

Instances of the class fail to validate, leading to runtime errors during instantiation.

Why It Broke

Namespace collision occurs when a class property shares a name with another class and is defined as Optional

Fix Options (Details)

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

pip install pydantic==1.10.14

When NOT to use: This fix should not be applied if the model structure is intentionally designed to allow such collisions.

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/8243

First fixed release: 1.10.14

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

When NOT to Use This Fix

This fix should not be applied if the model structure is intentionally designed to allow such collisions.

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
1.10.14	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error Data consistency OpenAPI schema

Sources

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

Pydantic Class properties have a potential for namespace collision (Fix)