Pydantic validate_call decorator does not work with

The Fix

Add support for `defer_build` with `@validate_call` decorator to resolve issues with static methods and class methods in Pydantic.

Based on closed pydantic/pydantic issue #11582 · 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

@@ -49,7 +49,18 @@ def wrapper_function(*args, **kwargs):
     """This is a wrapper around a function that validates the arguments passed to it, and optionally the return value."""
 
-    __slots__ = ('__pydantic_validator__', '__return_pydantic_validator__')
+    __slots__ = (
+        'function',

repro.py

from __future__ import (
    annotations,
)  # without this, there will be an error in static type-checking

from pydantic import BaseModel, Field, validate_call


class ClassA(BaseModel):

    field_a: int = Field(default=2)

    # EXPLICIT RETURN ClassA will lead to an error at runtime
    @classmethod
    @validate_call
    def does_not_work_1(
        cls,
        field_a: int,
    ) -> ClassA:
        return cls(field_a=field_a)

    # EXPLICIT RETURN ClassA will lead to an error at runtime
    @staticmethod
    @validate_call
    def does_not_work_2(
        field_a: int,
    ) -> ClassA:
        return ClassA(field_a=field_a)

    # NO ERROR
    @classmethod
    @validate_call
    def work_1(
        cls,
        field_a: int,
    ):
        return cls(field_a=field_a)

    # NO ERROR
    @staticmethod
    @validate_call
    def work_2(
        field_a: int,
    ):
        return ClassA(field_a=field_a)

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Apply the official fix\nAdd support for `defer_build` with `@validate_call` decorator to resolve issues with static methods and class methods in Pydantic.\nWhen NOT to use: Do not use this fix if the class structure is not defined at the module level.\n\nOption C — Workaround\nthis by setting [`defer_build`](https://docs.pydantic.dev/dev/api/config/#pydantic.config.ConfigDict.defer_build) to `True`. It currently has no effect for `@validate_call`, but I'm making a PR to make it work in 2.11:\nWhen NOT to use: Do not use this fix if the class structure is not defined at the module level.\n\n

Why This Fix Works in Production

Trigger: class ClassA(BaseModel):
Mechanism: The validate_call decorator fails with staticmethods/classmethods due to namespace resolution issues

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 validate_call decorator fails with staticmethods/classmethods due to namespace resolution issues
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #11582
Fix PR: https://github.com/pydantic/pydantic/pull/11584
Reproduced locally: No (not executed)
Last verified: 2026-02-11
Confidence: 0.80
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

“I have the same issue as indicated above”

@hqtuan99 · 2025-03-19 · source

“By the time the methods are defined, ClassA does not exist (as is it in the process of having its namespace defined)”

@Viicos · 2025-03-19 · source

Failure Signature (Search String)

class ClassA(BaseModel):

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "D:\crpatcher\test.py", line 6, in <module>
    class ClassA(BaseModel):
  File "D:\crpatcher\test.py", line 11, in ClassA       
    @validate_call
     ^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\validate_call_decorator.py", line 113, in validate_call   
    return validate(func)
           ^^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\validate_call_decorator.py", line 107, in validate        
    validate_call_wrapper = _validate_call.ValidateCallWrapper(
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\_internal\_validate_call.py", line 72, in __init__        
    schema = gen_schema.clean_schema(gen_schema.generate_schema(function))
                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\_internal\_generate_schema.py", line 610, in generate_schema
    schema = self._generate_schema_inner(obj)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\_internal\_generate_schema.py", line 884, in _generate_schema_inner
    return self.match_type(obj)
           ^^^^^^^^^^^^^^^^^^^^
  File "D:\crpatcher\.venv\Lib\site-packages\pydantic\_internal\_generate_schema.py", line 975, in match_type   
    return self.
... (truncated) ...

Minimal Reproduction

repro.py

from __future__ import (
    annotations,
)  # without this, there will be an error in static type-checking

from pydantic import BaseModel, Field, validate_call


class ClassA(BaseModel):

    field_a: int = Field(default=2)

    # EXPLICIT RETURN ClassA will lead to an error at runtime
    @classmethod
    @validate_call
    def does_not_work_1(
        cls,
        field_a: int,
    ) -> ClassA:
        return cls(field_a=field_a)

    # EXPLICIT RETURN ClassA will lead to an error at runtime
    @staticmethod
    @validate_call
    def does_not_work_2(
        field_a: int,
    ) -> ClassA:
        return ClassA(field_a=field_a)

    # NO ERROR
    @classmethod
    @validate_call
    def work_1(
        cls,
        field_a: int,
    ):
        return cls(field_a=field_a)

    # NO ERROR
    @staticmethod
    @validate_call
    def work_2(
        field_a: int,
    ):
        return ClassA(field_a=field_a)

Environment

Pydantic: 2

What Broke

Static methods using validate_call raise errors during schema generation, causing application failures.

Why It Broke

The validate_call decorator fails with staticmethods/classmethods due to namespace resolution issues

Fix Options (Details)

Option A — Apply the official fix

Add support for `defer_build` with `@validate_call` decorator to resolve issues with static methods and class methods in Pydantic.

When NOT to use: Do not use this fix if the class structure is not defined at the module level.

Option C — Workaround Temporary workaround

this by setting [`defer_build`](https://docs.pydantic.dev/dev/api/config/#pydantic.config.ConfigDict.defer_build) to `True`. It currently has no effect for `@validate_call`, but I'm making a PR to make it work in 2.11:

When NOT to use: Do not use this fix if the class structure is not defined at the module level.

Use only if you cannot change versions today. Treat this as a stopgap and remove once upgraded.

Fix reference: https://github.com/pydantic/pydantic/pull/11584

Last verified: 2026-02-11. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if the class structure is not defined at the module level.

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.

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 validate_call decorator does not work with staticmethod/classmethod that explicitly set (Fix)