Pydantic AttributeError when using __future_

The Fix

pip install pydantic==1.10.18

Based on closed pydantic/pydantic issue #10153 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -4,13 +4,14 @@
 import builtins
 import operator
+import sys
 import typing
 import warnings

repro.py

# from __future__ import annotations
import os

from pydantic import BaseModel, PrivateAttr
from typing_extensions import Annotated

class ParentModel(BaseModel):
    name: str
    age: int

class ChildModel(ParentModel):
    _cpu_count: Annotated[int, PrivateAttr(default_factory=os.cpu_count)]

child_instance = ChildModel(name="John Doe", age=30)
count = child_instance._cpu_count
print(count)
# > 16

# -----------------

from __future__ import annotations
import os

from pydantic import BaseModel, PrivateAttr
from typing_extensions import Annotated

class ParentModel(BaseModel):
    name: str
    age: int

class ChildModel(ParentModel):
    _cpu_count: Annotated[int, PrivateAttr(default_factory=os.cpu_count)]

child_instance = ChildModel(name="John Doe", age=30)
count = child_instance._cpu_count
print(count)

# >Traceback (most recent call last):
# >  File "/home/xx/xx/testing/venv/lib/python3.12/site-packages/pydantic/main.py", line 807, in # >__getattr__
# >    return self.__pydantic_private__[item]  # type: ignore
# >           ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
# >KeyError: '_cpu_count'
# >
# >The above exception was the direct cause of the following exception:
# >
# >Traceback (most recent call last):
# >  File "/home/xx/xx/testing/pydanticbugg.py", line 19, in <module>
# >    count = child_instance._cpu_count
# >            ^^^^^^^^^^^^^^^^^^^^^^^^^
# >  File "/home/xx/xx/testing/venv/lib/python3.12/site-packages/pydantic/main.py", line 809, in # >__getattr__
# >    raise AttributeError(f'{type(self).__name__!r} object has no attribute {item!r}') from exc
# > AttributeError: 'ChildModel' object has no attribute '_cpu_count'

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==1.10.18\nWhen NOT to use: This fix should not be used if the `Annotated` pattern is not supported by the type checker.\n\n

Why This Fix Works in Production

Trigger: AttributeError when using __future__ import with PrivateAttr in Pydantic
Mechanism: The `PrivateAttr` attribute does not initialize correctly when using `__future__` import for annotations
Why the fix works: Adds support for stringified annotations when using `PrivateAttr` with `Annotated`, resolving the AttributeError issue. (first fixed release: 1.10.18).

Why This Breaks in Prod

Shows up under Python 3.12 in real deployments (not just unit tests).
The `PrivateAttr` attribute does not initialize correctly when using `__future__` import for annotations
Surfaces as: AttributeError when using __future__ import with PrivateAttr in Pydantic

Proof / Evidence

GitHub issue: #10153
Fix PR: https://github.com/pydantic/pydantic/pull/10157
First fixed release: 1.10.18
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.44

Discussion

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

Jump to Sources Open on GitHub

“I would suggest avoiding the Annotated pattern for private attrs, as type checkers won't recognize them: But as it was supported in https://github.com/pydantic/pydantic/pull/8004, we'll have…”

@Viicos · 2024-08-16 · source

“Should be fixed by https://github.com/pydantic/pydantic/pull/10157”

@sydney-runkle · 2024-08-16 · source

Failure Signature (Search String)

AttributeError when using __future__ import with PrivateAttr in Pydantic

Error Message

Stack trace

error.txt

Error Message
-------------
AttributeError when using __future__ import with PrivateAttr in Pydantic

Minimal Reproduction

repro.py

# from __future__ import annotations
import os

from pydantic import BaseModel, PrivateAttr
from typing_extensions import Annotated

class ParentModel(BaseModel):
    name: str
    age: int

class ChildModel(ParentModel):
    _cpu_count: Annotated[int, PrivateAttr(default_factory=os.cpu_count)]

child_instance = ChildModel(name="John Doe", age=30)
count = child_instance._cpu_count
print(count)
# > 16

# -----------------

from __future__ import annotations
import os

from pydantic import BaseModel, PrivateAttr
from typing_extensions import Annotated

class ParentModel(BaseModel):
    name: str
    age: int

class ChildModel(ParentModel):
    _cpu_count: Annotated[int, PrivateAttr(default_factory=os.cpu_count)]

child_instance = ChildModel(name="John Doe", age=30)
count = child_instance._cpu_count
print(count)

# >Traceback (most recent call last):
# >  File "/home/xx/xx/testing/venv/lib/python3.12/site-packages/pydantic/main.py", line 807, in # >__getattr__
# >    return self.__pydantic_private__[item]  # type: ignore
# >           ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
# >KeyError: '_cpu_count'
# >
# >The above exception was the direct cause of the following exception:
# >
# >Traceback (most recent call last):
# >  File "/home/xx/xx/testing/pydanticbugg.py", line 19, in <module>
# >    count = child_instance._cpu_count
# >            ^^^^^^^^^^^^^^^^^^^^^^^^^
# >  File "/home/xx/xx/testing/venv/lib/python3.12/site-packages/pydantic/main.py", line 809, in # >__getattr__
# >    raise AttributeError(f'{type(self).__name__!r} object has no attribute {item!r}') from exc
# > AttributeError: 'ChildModel' object has no attribute '_cpu_count'

Environment

Python: 3.12
Pydantic: 2

What Broke

Users encounter an `AttributeError` when accessing private attributes in models with future annotations.

Why It Broke

The `PrivateAttr` attribute does not initialize correctly when using `__future__` import for annotations

Fix Options (Details)

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

pip install pydantic==1.10.18

When NOT to use: This fix should not be used if the `Annotated` pattern is not supported by the type checker.

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/10157

First fixed release: 1.10.18

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

When NOT to Use This Fix

This fix should not be used if the `Annotated` pattern is not supported by the type checker.

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
1.10.18	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 AttributeError when using __future__ import with PrivateAttr in Pydantic (Fix)