Pydantic Inconsistent Private Attribute Type (Fix)

The Fix

pip install pydantic==2.11.4

Based on closed pydantic/pydantic issue #11797 · 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

@@ -406,7 +406,7 @@ def inspect_namespace(  # noqa C901
             and value.__module__ == namespace['__module__']
             and '__qualname__' in namespace
-            and value.__qualname__.startswith(namespace['__qualname__'])
+            and value.__qualname__.startswith(f'{namespace["__qualname__"]}.')
         ):

repro.py

from enum import Enum
from pydantic import BaseModel


class HMSTablePrivilege(str, Enum):
    ALL_PRIVILEGES = "ALL PRIVILEGES"


class HMSTable(BaseModel):
    _grantable_privileges: Enum = HMSTablePrivilege


HMSTable._grantable_privileges
# <enum 'HMSTablePrivilege'>

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 private attributes are intended to remain inaccessible.\n\n

Why This Fix Works in Production

Trigger: Inconsistent Private Attribute Type
Mechanism: The qualified name comparison of private attributes during namespace inspection was incorrect
Why the fix works: Fixes the qualified name comparison of private attributes during namespace inspection, addressing the inconsistency in private attribute types. (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

The qualified name comparison of private attributes during namespace inspection was incorrect
Production symptom (often without a traceback): @karta9821 I appreciate the help but this is a genuine bug and what you stated is also incorrect.

Proof / Evidence

GitHub issue: #11797
Fix PR: https://github.com/pydantic/pydantic/pull/11803
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: 0.64

Verified Execution

We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.

Status: PASS
Ran: 2026-02-11T16:52:29Z
Package: pydantic
Fixed: 2.11.4
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

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

Jump to Sources Open on GitHub

“@karta9821 I appreciate the help but this is a genuine bug and what you stated is also incorrect. Offending code: https://github.com/pydantic/pydantic/blob/bf068661cf3fdadb93881762abe6fdc8a2592966/pydantic/_internal/_model_construction.py#L405-L412”

@Viicos · 2025-04-28 · source

“This is working as intended: Pydantic treats any attribute starting with an underscore as a private attribute, so it’s excluded entirely from schema generation, validation,…”

@karta9821 · 2025-04-27 · source

“@xinyang-zhu, note that we recommend inspecting private attributes using the __private_attributes__ class attribute. Trying to access by attribute name isn't explicitly supported.”

@Viicos · 2025-04-28 · source

Failure Signature (Search String)

Inconsistent Private Attribute Type

Copy-friendly signature

signature.txt

Failure Signature
-----------------
@karta9821 I appreciate the help but this is a genuine bug and what you stated is also incorrect.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
@karta9821 I appreciate the help but this is a genuine bug and what you stated is also incorrect.

Minimal Reproduction

repro.py

from enum import Enum
from pydantic import BaseModel


class HMSTablePrivilege(str, Enum):
    ALL_PRIVILEGES = "ALL PRIVILEGES"


class HMSTable(BaseModel):
    _grantable_privileges: Enum = HMSTablePrivilege


HMSTable._grantable_privileges
# <enum 'HMSTablePrivilege'>

Environment

Pydantic: 2

What Broke

Private attributes were inconsistently reported, leading to confusion in attribute access.

Why It Broke

The qualified name comparison of private attributes during namespace inspection was incorrect

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 private attributes are intended to remain inaccessible.

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/11803

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 private attributes are intended to remain inaccessible.

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.