Pydantic Bug: `TypeError: cannot pickle 'staticmethod'

The Fix

pip install pydantic==2.10.0

Based on closed pydantic/pydantic issue #10551 · 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

@@ -6,7 +6,7 @@
 from copy import copy
 from functools import lru_cache
-from inspect import Parameter, signature
+from inspect import Parameter, ismethoddescriptor, signature
 from typing import TYPE_CHECKING, Any, Callable, Pattern

repro.py

from collections.abc import Callable

from pydantic import BaseModel, Field


class SomeModel(BaseModel):
    @staticmethod
    def default_int_factory() -> int: ...

    # This is fine
    # int_factory: Callable[[], int] = default_int_factory
    # This blows up: TypeError: cannot pickle 'staticmethod' object
    int_factory: Callable[[], int] = Field(default=default_int_factory)

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==2.10.0\nWhen NOT to use: This fix should not be applied if the staticmethod is not intended for use as a default value.\n\n

Why This Fix Works in Production

Trigger: Bug: `TypeError: cannot pickle 'staticmethod' object` with a `Field.default`
Mechanism: Ensures that class access of method descriptors is performed when used as a default with `Field`, addressing the TypeError encountered with static methods.
Why the fix works: Ensures that class access of method descriptors is performed when used as a default with `Field`, addressing the TypeError encountered with static methods. (first fixed release: 2.10.0).

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

Triggered by an upgrade/regression window: 3.10 breaks; 2.10.0 is the first fixed release.
Shows up under Python 3.12 in real deployments (not just unit tests).
Surfaces as: Bug: `TypeError: cannot pickle 'staticmethod' object` with a `Field.default`

Proof / Evidence

GitHub issue: #10551
Fix PR: https://github.com/pydantic/pydantic/pull/10816
First fixed release: 2.10.0
Affected versions: 3.10
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.63

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: 2.10.0
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

“To me, I think bullet 1 sounds better because it seems: 1”

@jamesbraza · 2024-10-04 · source

“Related discussion for stdlib dataclasses: https://github.com/python/cpython/issues/102646”

@Viicos · 2024-11-11 · source

“Interesting things are happening here”

@Viicos · 2024-10-04 · source

Failure Signature (Search String)

Bug: `TypeError: cannot pickle 'staticmethod' object` with a `Field.default`

Error Message

Stack trace

error.txt

Error Message
-------------
Bug: `TypeError: cannot pickle 'staticmethod' object` with a `Field.default`

Minimal Reproduction

repro.py

from collections.abc import Callable

from pydantic import BaseModel, Field


class SomeModel(BaseModel):
    @staticmethod
    def default_int_factory() -> int: ...

    # This is fine
    # int_factory: Callable[[], int] = default_int_factory
    # This blows up: TypeError: cannot pickle 'staticmethod' object
    int_factory: Callable[[], int] = Field(default=default_int_factory)

Environment

Python: 3.12
Pydantic: 2

What Broke

Users encounter a TypeError when attempting to use staticmethods as default values in Pydantic models.

Fix Options (Details)

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

pip install pydantic==2.10.0

When NOT to use: This fix should not be applied if the staticmethod is not intended for use as a default value.

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/10816

First fixed release: 2.10.0

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

When NOT to Use This Fix

This fix should not be applied if the staticmethod is not intended for use as a default value.

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
3.10	Broken
2.10.0	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.

Pydantic Bug: `TypeError: cannot pickle 'staticmethod' object` with a `Field.default` (Fix)