ruff format removes except-clause parentheses under py314

Agent diagnostic brief

Exact symptom

except TypeError, ValueError:

Where it has been observed

Python project with [tool.ruff] target-version = "py314"; except clauses without an `as` binding.

Likely distinct causes

The formatter normalizes the clause under a py314 target.
The edit was never saved: check the file immediately after editing.
Another commit reverted it: check the history.

How to distinguish them

Edit, run ruff format, and grep: the parentheses disappear only after formatting.
Repeat with target-version py313: the parentheses remain.
Check whether the clause has an `as` binding.

Current approaches

Accept the PEP 758 form under py314 or lower the target (solution-ruff-pep758-except-parentheses, revision 1).

Known obsolete approaches

Re-applying the parentheses by hand under a py314 target.

Versions and freshness

Observed with ruff 0.15.12 on 2026-09-08; reproduced with ruff 0.16.7 on 2026-09-11; behavior introduced in ruff 0.15.0
Editorial and primary-source review date: 2026-09-11.

What remains unknown

Whether ruff will add an option to keep the parentheses.
Independent reproduction by a different operator has not been established.

Deeper evidence

Problem

ruff format removes except-clause parentheses under py314

Observed symptom

An edit that parenthesizes a multi-exception except clause keeps disappearing: `ruff format` with target-version py314 rewrites it to the PEP 758 unparenthesized form, so reviewers report the fix as never applied.
This historical observation is same-operator evidence and does not establish prevalence.

Operator goal

Apply a review request to parenthesize a multi-exception except clause.

Current understanding

PEP 758 (Python 3.14) allows `except A, B:` without parentheses when there is no `as` binding.
Since ruff 0.15.0 the formatter enforces that style when target-version is 3.14 or later; clauses with `as` keep their parentheses.

Known limitations

Upstream issues discuss surprises in mixed-tooling setups; behavior may be refined in later releases.

Known negative results

Keep re-applying the parentheses. Result: The formatter removed them on every verification pass and hand-parenthesized code fails `ruff format --check`. Why it misleads: Under a py314 target the unparenthesized form is the formatter's canonical style.
No same-operator execution in this release counts as an independent reproduction.

Primary and recurrence sources

PEP 758: except without parentheses
Primary · Primary specification · Date not supplied · Reviewed 2026-09-11 · Rights: allowed_to_summarize
Current primary material reviewed for claude-historical-corpus-1: PEP 758: except without parentheses.
Ruff v0.15.0 release notes
Primary · Primary release notes · Date not supplied · Reviewed 2026-09-11 · Rights: allowed_to_summarize
Current primary material reviewed for claude-historical-corpus-1: Ruff v0.15.0 release notes.

Rights and provenance

Origin

Based on a real operator execution; identifying project details removed.

Rights

State: allowed_to_summarize
Review basis: Owner-authorized factual synthesis of the operator's own Claude-assisted execution, independently written from reviewed current primary sources; no transcript expression is published.

Editorial review date

2026-09-11

Known approaches

solution · Revision 1

Accept the PEP 758 form under py314 or lower the target

Production corpus importer · 2026-09-11T20:00:00.000Z
Operator Knowledge for Agents editorial · Historical operator record · Digital source: trainedAlgorithmicMedia · Rights: owned

## Candidate action - Accept the PEP 758 form under py314 or lower the target. Accept the formatter's PEP 758 form under a py314 target (clauses with `as` keep parentheses), or lower the target if any tooling still parses with Python 3.13 or older. This is a candidate procedure supported by same-operator executions within the stated version boundary, not a universal fix. ## Applicability - Use when the observed signature is: except TypeError, ValueError:. - Observed scope: Python project with [tool.ruff] target-version = "py314"; except clauses without an `as` binding. - Stop if the first failing stage or product boundary differs. ## Procedure - Confirm the project's target-version. - If every tool that parses the code supports Python 3.14, keep the formatter's form and note it for reviewers. - If any tool still parses with Python 3.13 or older, lower target-version instead of fighting the formatter. - Re-run `ruff format --check` to confirm the result is stable. ## Limitations - Upstream issues discuss surprises in mixed-tooling setups; behavior may be refined in later releases. ## Obsolete approaches - Re-applying the parentheses by hand under a py314 target. ## Negative results - Keep re-applying the parentheses. Result: The formatter removed them on every verification pass and hand-parenthesized code fails `ruff format --check`. Why it misleads: Under a py314 target the unparenthesized form is the formatter's canonical style. - No external or same-operator report was promoted to independent reproduction credit. ## Evidence boundary - Grounded in current primary source records src-pep-758, src-ruff-v0150-release. - Grade A same-operator observation (2026-09-08): Two independent reproductions showed ruff removing the parentheses only under target-version py314; under py313/py311 they survived, and the formatter-enforced form was accepted. - Only immutable manifest executions count as Knowledge for Agents Attempts or Outcomes. ## What remains unknown - Whether ruff will add an option to keep the parentheses. - Whether the approach works outside the stated environment remains unknown.

Candidate id

claude-ruff-pep758-except-parentheses

Historical period

2026-09-08

Historical date

2026-09-08

Verification grade

Operator relationship

same_operator

Independent reproduction

false

History source

same-operator Claude agent session history

Provenance disclosure

Based on a real operator execution; identifying project details removed.

Applicability

State

partial

Text

Applies when the failed stage matches: except TypeError, ValueError:.

Facts

Component: formatter target-version
Operation: parenthesize a multi-exception except clause
Protocol: Python 3.14 grammar (PEP 758)

Pack

Candidate action: Accept the PEP 758 form under py314 or lower the target. Accept the formatter's PEP 758 form under a py314 target (clauses with `as` keep parentheses), or lower the target if any tooling still parses with Python 3.13 or older. This is a candidate procedure supported by same-operator executions within the stated version boundary, not a universal fix.
Applicability: Use when the observed signature is: except TypeError, ValueError:.
Observed scope: Python project with [tool.ruff] target-version = "py314"; except clauses without an `as` binding.
Stop if the first failing stage or product boundary differs.
Steps: Confirm the project's target-version.
If every tool that parses the code supports Python 3.14, keep the formatter's form and note it for reviewers.
If any tool still parses with Python 3.13 or older, lower target-version instead of fighting the formatter.
Re-run `ruff format --check` to confirm the result is stable.
Limitations: Upstream issues discuss surprises in mixed-tooling setups; behavior may be refined in later releases.
Obsolete approaches: Re-applying the parentheses by hand under a py314 target.
Negative results: Keep re-applying the parentheses. Result: The formatter removed them on every verification pass and hand-parenthesized code fails `ruff format --check`. Why it misleads: Under a py314 target the unparenthesized form is the formatter's canonical style.
No external or same-operator report was promoted to independent reproduction credit.
Evidence boundary: Grounded in current primary source records src-pep-758, src-ruff-v0150-release.
Grade A same-operator observation (2026-09-08): Two independent reproductions showed ruff removing the parentheses only under target-version py314; under py313/py311 they survived, and the formatter-enforced form was accepted.
Only immutable manifest executions count as Knowledge for Agents Attempts or Outcomes.
What remains unknown: Whether ruff will add an option to keep the parentheses.
Whether the approach works outside the stated environment remains unknown.

Rights

State: allowed_to_summarize
Review basis: Original diagnostic procedure synthesized from owner-authorized execution facts and linked current primary sources; no private source code, logs, or transcript expression is published.

Source ids

src-pep-758
src-ruff-v0150-release

Editorial review date

2026-09-11

Seo metadata

Meta title: Accept the PEP 758 form under py314 or lower the target | Knowledge for Agents
Meta description: Candidate procedure for ruff format removes except-clause parentheses under py314: applicability, steps, current sources, limitations, negative results, and unknowns.

Historical execution

Disclosure: Based on a real operator execution; identifying project details removed.
Operator relationship: same_operator
Independent reproduction: false

Problem id

problem-ruff-pep758-except-parentheses

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Sources and related records

No source relations recorded.