[`pyflakes`] Skip `undefined-name` (`F821`) for conditionally deleted variables by dylwil3 · Pull Request #24088 · astral-sh/ruff

dylwil3 · 2026-03-20T18:50:35Z

We already skip F821 for things like this:

x = 1
if cond:
    del x
print(x) # no diagnostic here

But when we checked for "conditional branches" we were only looking for match, if, and while statements:

ruff/crates/ruff_python_ast/src/helpers.rs

Lines 1110 to 1128 in f32b9bb

    
           /// Check if a node is part of a conditional branch. 
        
           pub fn on_conditional_branch<'a>(parents: &mut impl Iterator<Item = &'a Stmt>) -> bool { 
        
               parents.any(|parent| { 
        
                   if matches!(parent, Stmt::If(_) | Stmt::While(_) | Stmt::Match(_)) { 
        
                       return true; 
        
                   } 
        
                   if let Stmt::Expr(ast::StmtExpr { 
        
                       value, 
        
                       range: _, 
        
                       node_index: _, 
        
                   }) = parent 
        
                   { 
        
                       if value.is_if_expr() { 
        
                           return true; 
        
                       } 
        
                   } 
        
                   false 
        
               }) 
        
           }

Here we also check for except handlers and else clauses. We continue to regard try statements as "unconditionally executing" even though that's not quite true.

Closes #6242

As an aside: I originally wanted to use the BindingKind variant ConditionalDeletion introduced way back in #10415, but it turns out we never actually constructed an instance of it! We could, if we ever needed to track the "thing that was conditionally deleted". But since that doesn't seem to have ever arisen in practice, I just got rid of the variant and its references altogether.

astral-sh-bot · 2026-03-20T19:05:05Z

`ruff-ecosystem` results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+4 -0 violations, +0 -0 fixes in 1 projects; 55 projects unchanged)

prefecthq/prefect (+4 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --no-fix --output-format concise --preview

+ src/prefect/_internal/concurrency/calls.py:432:45: RUF100 [*] Unused `noqa` directive (unused: `F821`)
+ src/prefect/_internal/concurrency/calls.py:433:53: RUF100 [*] Unused `noqa` directive (unused: `F821`)
+ src/prefect/_internal/concurrency/calls.py:467:45: RUF100 [*] Unused `noqa` directive (unused: `F821`)
+ src/prefect/_internal/concurrency/calls.py:468:59: RUF100 [*] Unused `noqa` directive (unused: `F821`)

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
RUF100	4	4	0	0	0

@bitloi

##### [\`v0.15.8\`](https://github.com/astral-sh/ruff/blob/HEAD/CHANGELOG.md#0158) Released on 2026-03-26. ##### Preview features - \[`ruff`] New rule `unnecessary-if` (`RUF050`) ([#24114](astral-sh/ruff#24114)) - \[`ruff`] New rule `useless-finally` (`RUF072`) ([#24165](astral-sh/ruff#24165)) - \[`ruff`] New rule `f-string-percent-format` (`RUF073`): warn when using `%` operator on an f-string ([#24162](astral-sh/ruff#24162)) - \[`pyflakes`] Recognize `frozendict` as a builtin for Python 3.15+ ([#24100](astral-sh/ruff#24100)) ##### Bug fixes - \[`flake8-async`] Use fully-qualified `anyio.lowlevel` import in autofix (`ASYNC115`) ([#24166](astral-sh/ruff#24166)) - \[`flake8-bandit`] Check tuple arguments for partial paths in `S607` ([#24080](astral-sh/ruff#24080)) - \[`pyflakes`] Skip `undefined-name` (`F821`) for conditionally deleted variables ([#24088](astral-sh/ruff#24088)) - `E501`/`W505`/formatter: Exclude nested pragma comments from line width calculation ([#24071](astral-sh/ruff#24071)) - Fix `%foo?` parsing in IPython assignment expressions ([#24152](astral-sh/ruff#24152)) - `analyze graph`: resolve string imports that reference attributes, not just modules ([#24058](astral-sh/ruff#24058)) ##### Rule changes - \[`eradicate`] ignore `ty: ignore` comments in `ERA001` ([#24192](astral-sh/ruff#24192)) - \[`flake8-bandit`] Treat `sys.executable` as trusted input in `S603` ([#24106](astral-sh/ruff#24106)) - \[`flake8-self`] Recognize `Self` annotation and `self` assignment in `SLF001` ([#24144](astral-sh/ruff#24144)) - \[`pyflakes`] `F507`: Fix false negative for non-tuple RHS in `%`-formatting ([#24142](astral-sh/ruff#24142)) - \[`refurb`] Parenthesize generator arguments in `FURB142` fixer ([#24200](astral-sh/ruff#24200)) ##### Performance - Speed up diagnostic rendering ([#24146](astral-sh/ruff#24146)) ##### Server - Warn when Markdown files are skipped due to preview being disabled ([#24150](astral-sh/ruff#24150)) ##### Documentation - Clarify `extend-ignore` and `extend-select` settings documentation ([#24064](astral-sh/ruff#24064)) - Mention AI policy in PR template ([#24198](astral-sh/ruff#24198)) ##### Other changes - Use trusted publishing for NPM packages ([#24171](astral-sh/ruff#24171)) ##### Contributors - [@bitloi](https://github.com/bitloi) - [@Sim-hu](https://github.com/Sim-hu) - [@mvanhorn](https://github.com/mvanhorn) - [@chinar-amrutkar](https://github.com/chinar-amrutkar) - [@markjm](https://github.com/markjm) - [@RenzoMXD](https://github.com/RenzoMXD) - [@vivekkhimani](https://github.com/vivekkhimani) - [@seroperson](https://github.com/seroperson) - [@moktamd](https://github.com/moktamd) - [@charliermarsh](https://github.com/charliermarsh) - [@ntBre](https://github.com/ntBre) - [@zanieb](https://github.com/zanieb) - [@dylwil3](https://github.com/dylwil3) - [@MichaReiser](https://github.com/MichaReiser) Renovate-Branch: renovate/2024.6-ruff-0.15.x Change-Id: Ifd4216a963962ffb24a4df69802bc60fcc29628d Priv-Id: 46d2f61be3a5e65a9fdd2fef998ba41ea3388f12

dylwil3 added 5 commits March 20, 2026 13:26

add failing test

ede8f50

skip deletions inside except handlers as conditional

e43d30f

add semantic flag for in orelse clause

91e3bd7

record whether we are in orelse clause

5922957

test conditional deletion in orelse clause

e3b9e70

dylwil3 added bug Something isn't working rule Implementing or modifying a lint rule labels Mar 20, 2026

remove never used BindingKind::ConditionalDeletion

0c34a16

dylwil3 marked this pull request as ready for review March 20, 2026 19:02

astral-sh-bot bot assigned ntBre Mar 20, 2026

astral-sh-bot bot requested a review from ntBre March 20, 2026 19:02

dylwil3 removed the request for review from ntBre March 20, 2026 22:41

dylwil3 unassigned ntBre Mar 20, 2026

charliermarsh approved these changes Mar 21, 2026

View reviewed changes

dylwil3 merged commit 1a2e402 into astral-sh:main Mar 21, 2026
42 checks passed

dylwil3 deleted the try-else-undefined branch March 21, 2026 13:17

dylwil3 mentioned this pull request Mar 24, 2026

wrong F821 hits #24158

Closed

BrewTestBot mentioned this pull request Mar 26, 2026

ruff 0.15.8 Homebrew/homebrew-core#274426

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[`pyflakes`] Skip `undefined-name` (`F821`) for conditionally deleted variables#24088

[`pyflakes`] Skip `undefined-name` (`F821`) for conditionally deleted variables#24088
dylwil3 merged 6 commits intoastral-sh:mainfrom
dylwil3:try-else-undefined

dylwil3 commented Mar 20, 2026 •

edited

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	/// Check if a node is part of a conditional branch.
	pub fn on_conditional_branch<'a>(parents: &mut impl Iterator<Item = &'a Stmt>) -> bool {
	parents.any(\|parent\| {
	if matches!(parent, Stmt::If(_) \| Stmt::While(_) \| Stmt::Match(_)) {
	return true;
	}
	if let Stmt::Expr(ast::StmtExpr {
	value,
	range: _,
	node_index: _,
	}) = parent
	{
	if value.is_if_expr() {
	return true;
	}
	}
	false
	})
	}

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dylwil3 commented Mar 20, 2026 •

edited

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