Pydantic 2.10: `mypy` (with pydantic.mypy) complains about

The Fix

pip install pydantic==2.10.3

Based on closed pydantic/pydantic issue #10945 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -571,6 +571,15 @@ def deprecation_message(self) -> str | None:
         return self.deprecated if isinstance(self.deprecated, str) else self.deprecated.message
 
+    @property
+    def default_factory_takes_validated_data(self) -> bool | None:
+        """Whether the provided default factory callable has a validated data parameter.

repro.py

@override
    def get_raw(self, item: str) -> Any:
        if item in self._cache:
            return self._cache[item]
        field = self._config_model.model_fields[item]
        if not field.is_required():
            self._cache[item] = field.get_default(call_default_factory=True)
        else:
            raise KeyError(f"config item {item!r} has no default value.")

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==2.10.3\nWhen NOT to use: This fix is not applicable if the default factory does not require validated_data.\n\n

Why This Fix Works in Production

Trigger: with the latest version of pydantic (`2.10.1`) and the mypy plugin, we observe some false positive with type validation.
Mechanism: The default factory in Pydantic now accepts a validated_data argument, causing mypy to raise false positives
Why the fix works: Add a property to check if the default factory callable has a validated data parameter, addressing the issue with mypy false positives. (first fixed release: 2.10.3).

Why This Breaks in Prod

Shows up under Python 3.11 in real deployments (not just unit tests).
The default factory in Pydantic now accepts a validated_data argument, causing mypy to raise false positives
Production symptom (often without a traceback): with the latest version of pydantic (`2.10.1`) and the mypy plugin, we observe some false positive with type validation.

Proof / Evidence

GitHub issue: #10945
Fix PR: https://github.com/pydantic/pydantic/pull/11034
First fixed release: 2.10.3
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.59

Discussion

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

Jump to Sources Open on GitHub

“This is odd bc default_factory is typed as Callable[[], Any] | Callable[[dict[str, Any]], Any] | None”

@sydney-runkle · 2024-11-22 · source

“@Viicos i think your reply is not related to this issue.”

@l00ptr · 2024-11-28 · source

“Yes sorry I went to see the PR that mentioned the issue and thought it was the same person that raised it. In your case,…”

@Viicos · 2024-11-28 · source

“In 2.10, default factories may accept a new validated_data argument”

@Viicos · 2024-11-26 · source

Failure Signature (Search String)

with the latest version of pydantic (`2.10.1`) and the mypy plugin, we observe some false positive with type validation.
When running mypy over that piece of code, we observe that kind of error:

Copy-friendly signature

signature.txt

Failure Signature
-----------------
with the latest version of pydantic (`2.10.1`) and the mypy plugin, we observe some false positive with type validation.
When running mypy over that piece of code, we observe that kind of error:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
with the latest version of pydantic (`2.10.1`) and the mypy plugin, we observe some false positive with type validation.
When running mypy over that piece of code, we observe that kind of error:

Minimal Reproduction

repro.py

@override
    def get_raw(self, item: str) -> Any:
        if item in self._cache:
            return self._cache[item]
        field = self._config_model.model_fields[item]
        if not field.is_required():
            self._cache[item] = field.get_default(call_default_factory=True)
        else:
            raise KeyError(f"config item {item!r} has no default value.")

Environment

Python: 3.11
Pydantic: 2

What Broke

Mypy reports false positive errors regarding default factory arguments during type validation.

Why It Broke

The default factory in Pydantic now accepts a validated_data argument, causing mypy to raise false positives

Fix Options (Details)

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

pip install pydantic==2.10.3

When NOT to use: This fix is not applicable if the default factory does not require validated_data.

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/11034

First fixed release: 2.10.3

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

When NOT to Use This Fix

This fix is not applicable if the default factory does not require validated_data.

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
2.10.3	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:caching Pydantic hub Pydantic best practices All hubs All clusters

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 2.10: `mypy` (with pydantic.mypy) complains about Too few arguments on default factory (Fix)