Pydantic `cached_property` cannot be assigned by

The Fix

pip install pydantic==1.10.19

Based on closed pydantic/pydantic issue #10772 · 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

@@ -8,6 +8,7 @@
 import warnings
 from copy import copy, deepcopy
+from functools import cached_property
 from typing import (
     TYPE_CHECKING,

repro.py

from pydantic import (
    BaseModel,
    ConfigDict,
    Field,
    computed_field,
    field_serializer,
    model_validator,
)


@dataclass
class CreateCouponInput:
    user_id: str
    coupon_id: str
    amount: int

    @computed_field(return_type=int)
    @functools.cached_property
    def sss(self):
        return "haha"


c = CreateCouponInput(user_id="1", coupon_id="2", amount=3)
c.sss = 2

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==1.10.19\nWhen NOT to use: This fix should not be used if the model relies on strict property behavior.\n\n

Why This Fix Works in Production

Trigger: `cached_property` cannot be assigned by recommended way
Mechanism: The `cached_property` does not control attribute assignment behavior in Pydantic models
Why the fix works: Ensures that `cached_property` can be set on Pydantic models, addressing the issue where assignment was not working as expected. (first fixed release: 1.10.19).

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

Shows up under Python 3.10 in real deployments (not just unit tests).
The `cached_property` does not control attribute assignment behavior in Pydantic models
Production symptom (often without a traceback): `cached_property` cannot be assigned by recommended way

Proof / Evidence

GitHub issue: #10772
Fix PR: https://github.com/pydantic/pydantic/pull/10774
First fixed release: 1.10.19
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.66

Discussion

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

Jump to Sources Open on GitHub

“Indeed, this is annoying”

@Viicos · 2024-11-06 · source

Failure Signature (Search String)

`cached_property` cannot be assigned by recommended way

Copy-friendly signature

signature.txt

Failure Signature
-----------------
`cached_property` cannot be assigned by recommended way

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
`cached_property` cannot be assigned by recommended way

Minimal Reproduction

repro.py

from pydantic import (
    BaseModel,
    ConfigDict,
    Field,
    computed_field,
    field_serializer,
    model_validator,
)


@dataclass
class CreateCouponInput:
    user_id: str
    coupon_id: str
    amount: int

    @computed_field(return_type=int)
    @functools.cached_property
    def sss(self):
        return "haha"


c = CreateCouponInput(user_id="1", coupon_id="2", amount=3)
c.sss = 2

Environment

Python: 3.10
Pydantic: 2

What Broke

Attempting to assign a value to a `cached_property` results in an AttributeError.

Why It Broke

The `cached_property` does not control attribute assignment behavior in Pydantic models

Fix Options (Details)

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

pip install pydantic==1.10.19

When NOT to use: This fix should not be used if the model relies on strict property behavior.

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/10774

First fixed release: 1.10.19

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

When NOT to Use This Fix

This fix should not be used if the model relies on strict property behavior.

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
1.10.19	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 `cached_property` cannot be assigned by recommended way (Fix)