The Fix
pip install pydantic==1.10.15
Based on closed pydantic/pydantic issue #9375 · PR/commit linked
@@ -32,6 +32,7 @@ _build/
.coverage
test.py
+run_mypy_on_file.py
# Documentation files
repro.py
from enum import Enum
from pydantic import TypeAdapter
class MyEnum(Enum):
A = 1
B = 2
ta = TypeAdapter(MyEnum)
assert ta.validate_python(1.0) is MyEnum.A
assert ta.validate_python(2.0) is MyEnum.B
# pydantic=2.6.4 passes validation
# pydantic=2.7.1 fails validation
#
# pydantic_core._pydantic_core.ValidationError: 1 validation error for enum[MyEnum]
# Input should be 1, 2 or 3 [type=enum, input_value=1.0, input_type=float]
# For further information visit https://errors.pydantic.dev/2.7/v/enum
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==1.10.15\nWhen NOT to use: Do not use this fix if your application relies on float values being accepted by enums.\n\nOption B — Safe version pin\npip install pydantic==2.6.4\nWhen NOT to use: Do not use if you need features or security fixes in newer releases.\n\n
Why This Fix Works in Production
- Trigger: Enum construction from float worked in v2.6.4 but fails in v2.7.1
- Why the fix works: the upstream fix ships in 1.10.15.
Why This Breaks in Prod
- Triggered by an upgrade/regression window: 2.7.1 breaks; 1.10.15 is the first fixed release.
- Production symptom (often without a traceback): Enum construction from float worked in v2.6.4 but fails in v2.7.1
Proof / Evidence
- GitHub issue: #9375
- Fix PR: https://github.com/pydantic/pydantic/pull/9064
- First fixed release: 1.10.15
- Affected versions: 2.7.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.70
- 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).
“@Idealcoder, Thanks for reporting this. Looks like a regression we should fix in 2.7.2. Adding this to the relevant milestone. Just got back form a…”
Failure Signature (Search String)
- Enum construction from float worked in v2.6.4 but fails in v2.7.1
- Constructing an enum from a float worked in v2.6.4 but fails in v2.7.1.
Copy-friendly signature
signature.txt
Failure Signature
-----------------
Enum construction from float worked in v2.6.4 but fails in v2.7.1
Constructing an enum from a float worked in v2.6.4 but fails in v2.7.1.
Error Message
Signature-only (no traceback captured)
error.txt
Error Message
-------------
Enum construction from float worked in v2.6.4 but fails in v2.7.1
Constructing an enum from a float worked in v2.6.4 but fails in v2.7.1.
Minimal Reproduction
repro.py
from enum import Enum
from pydantic import TypeAdapter
class MyEnum(Enum):
A = 1
B = 2
ta = TypeAdapter(MyEnum)
assert ta.validate_python(1.0) is MyEnum.A
assert ta.validate_python(2.0) is MyEnum.B
# pydantic=2.6.4 passes validation
# pydantic=2.7.1 fails validation
#
# pydantic_core._pydantic_core.ValidationError: 1 validation error for enum[MyEnum]
# Input should be 1, 2 or 3 [type=enum, input_value=1.0, input_type=float]
# For further information visit https://errors.pydantic.dev/2.7/v/enum
Environment
- Pydantic: 2
What Broke
Users experienced validation errors when passing float values to enums, leading to application crashes.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==1.10.15
When NOT to use: Do not use this fix if your application relies on float values being accepted by enums.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option B — Safe version pin Backward-compatible pin
pip install pydantic==2.6.4
When NOT to use: Do not use if you need features or security fixes in newer releases.
Use when you can’t upgrade immediately. Plan a follow-up to upgrade (pins can accumulate security/compat debt).
Option D — Guard side-effects with OnceOnly Guardrail for side-effects
Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.
- Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
- Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
- Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.
Show example snippet (optional)
onceonly.py
from onceonly import OnceOnly
import os
once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)
# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..." # replace
key = f"stripe:webhook:{event_id}"
res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
return {"status": "already_processed"}
# Safe to execute the side-effect exactly once.
handle_event(event_id)
When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Fix reference: https://github.com/pydantic/pydantic/pull/9064
First fixed release: 1.10.15
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if your application relies on float values being accepted by enums.
- Do not use if you need features or security fixes in newer releases.
- Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
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 |
|---|---|
| 2.6.4 | Working |
| 2.7.1 | Broken |
| 1.10.15 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.