The Fix
pip install pydantic==1.10.1
Based on closed pydantic/pydantic issue #9259 · 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%.
@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Support instance methods and class methods with `@validate_arguments`
diff --git a/pydantic/decorator.py b/pydantic/decorator.py
index 94e684f8d8d..d99ab1d556f 100644
from pydantic import BaseModel
class Message(BaseModel):
recipient: int
Message(recipient="+1")
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
Option A — Upgrade to fixed release\npip install pydantic==1.10.1\nWhen NOT to use: This fix should not be applied if the parsing behavior for other formats is required.\n\n
Why This Fix Works in Production
- Trigger: v2.7 validation error when integer starts with `+`
- Mechanism: Parsing integers starting with a unary plus fails due to changes in int parsing
- Why the fix works: Fix parsing of integers starting with a unary plus in Pydantic v2.7.0. (first fixed release: 1.10.1).
- 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 3.11 in real deployments (not just unit tests).
- Parsing integers starting with a unary plus fails due to changes in int parsing
- Production symptom (often without a traceback): v2.7 validation error when integer starts with `+`
Proof / Evidence
- GitHub issue: #9259
- Fix PR: https://github.com/pydantic/pydantic-core/pull/1272
- First fixed release: 1.10.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.80
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.67
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: 1.10.1
- Mode: fixed_only
- Outcome: ok
Logs
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“@cknv, Thanks for the report. Looks like it should be an easy fix in pydantic-core, I'll work on that for our patch release!”
“Since it seemed easy @sydney-runkle I gave it a shot in https://github.com/pydantic/pydantic-core/pull/1272.”
“@cknv, Amazing, great work. @davidhewitt left a small comment / suggestion - once you resolve that, we can merge :).”
Failure Signature (Search String)
- v2.7 validation error when integer starts with `+`
- Parsing integers starting with unary plus (such as `+1`) fails to parse to an int using pydantic v2.7.0 - found it from a test that broke when trying to upgrade dependencies.
Copy-friendly signature
Failure Signature
-----------------
v2.7 validation error when integer starts with `+`
Parsing integers starting with unary plus (such as `+1`) fails to parse to an int using pydantic v2.7.0 - found it from a test that broke when trying to upgrade dependencies.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
v2.7 validation error when integer starts with `+`
Parsing integers starting with unary plus (such as `+1`) fails to parse to an int using pydantic v2.7.0 - found it from a test that broke when trying to upgrade dependencies.
Minimal Reproduction
from pydantic import BaseModel
class Message(BaseModel):
recipient: int
Message(recipient="+1")
Environment
- Python: 3.11
- Pydantic: 2
What Broke
Users experience validation errors when providing integers with a unary plus.
Why It Broke
Parsing integers starting with a unary plus fails due to changes in int parsing
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==1.10.1
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/pydantic/pydantic-core/pull/1272
First fixed release: 1.10.1
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be applied if the parsing behavior for other formats is required.
Verify Fix
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 |
|---|---|
| 1.10.1 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.