# ruff F632: fix changes program behavior Internal evidence sheet generated by fixhunt. Not an issue text. A human re-verifies, checks the duplicates below, and writes the upstream report in their own words following the project's AI policy. - Tool: ruff ruff 0.17.1 - Rule: F632 (tool labels the fix: unknown, this fix reported as safe) - Oracle: fix-changes-behavior - Judge (Nemotron 3 Ultra, advisory): intended-change, severity high. The rule rewrites `x is []` to `x == []`, changing an identity comparison to a value comparison. The documentation explicitly states that `is` with literals is incorrect and that `==` should be used instead, so the behavioral change (from False to True) is exactly the semantic change the rule intends. - Program: minimized from 9 to 6 lines ## Reproducer ```python __all__ = ['x'] x = [] if x is []: print('same object') del x from __main__ import * ``` ## Commands ```sh python3 prog.py ruff check --preview --isolated --select F632 --fix prog.py python3 prog.py ``` ## Observed ``` stdout before: stdout after: same object ``` ## Diff applied by the fix ```diff --- orig.py 2026-10-22 13:34:17.421862621 -0400 +++ fixed.py 2026-10-22 13:34:19.520897989 -0400 @@ -1,6 +1,6 @@ __all__ = ['x'] x = [] -if x is []: +if x == []: print('same object') del x from __main__ import * ``` ## Why the rewrite is not equivalent (model draft, verify before use) The original condition `x is []` checks identity; since each literal `[]` creates a new list object, it evaluates to False, so nothing prints. After rewriting to `x == []`, equality compares contents—both lists are empty—so True triggers printing 'same object'. Thus behavior changes because identity versus value equality differ for mutable objects like lists. No other modifications affect output. ## Upstream search Queries: "F632 fix", "F632 identity comparison list literal", "is empty list check replacement", "list equality vs identity lint" - related: https://github.com/astral-sh/ruff/issues/12518 Same rule F632 but different construct: False == 0 comparison instead of list identity check. - related: https://github.com/astral-sh/ruff/issues/11736 Same rule F632 but different trigger: panic on invalid syntax rather than behavior-changing fix. - related: https://github.com/astral-sh/ruff/issues/9374 Same rule F632 but different defect: infinite loop between == and is on chained comparisons. - duplicate: https://github.com/astral-sh/ruff/issues/8589 Same rule F632 and same construct: 'variable is []' identity comparison being incorrectly rewritten to '== []'. - related: https://github.com/astral-sh/ruff/issues/6891 Same rule F632 but different defect: infinite loop with E712 on generator expressions. - related: https://github.com/astral-sh/ruff/issues/1057 Same rule F632 but different construct: 'value % 2 is 0' modulo comparison causing fix panic. - related: https://github.com/astral-sh/ruff/pull/8607 Same rule F632 but different construct: 'None is False' constant comparison stabilization. - related: https://github.com/astral-sh/ruff/pull/12049 Same rule F632 but broader stabilization work on 'is' comparisons to lists, not the specific behavior-change fix.
All hits - [github, closed] unused-function-argument not silenced by prefixed underscore if variable name is "次" — https://github.com/astral-sh/ruff/issues/28721 - [github, open] Implement Pylint — https://github.com/astral-sh/ruff/issues/970 - [github, closed] Isort rule misses unsorted imports when using user-level ruff.toml file on windows — https://github.com/astral-sh/ruff/issues/19646 - [github, closed] [Feature Idea] Add column headers to `ruff check --statistics`, to avoid ambiguity — https://github.com/astral-sh/ruff/issues/13717 - [github, closed] F632 suggestion leads to false positive when comparing False == 0 — https://github.com/astral-sh/ruff/issues/12518 - [github, closed] Rule F632 cause panic — https://github.com/astral-sh/ruff/issues/11736 - [github, closed] [QA] Should Ruff be able to fix indentation errors (E999) ? — https://github.com/astral-sh/ruff/issues/11846 - [github, closed] Infinite loop in F632/E711 — https://github.com/astral-sh/ruff/issues/9374 - [github, closed] Catch `variable is []` — https://github.com/astral-sh/ruff/issues/8589 - [github, closed] Rules E712,F632 causes infinite loop — https://github.com/astral-sh/ruff/issues/6891 - [tavily] [bug] ruff chokes when fixing invalid comparison (`F632`) · Issue #1057 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/1057 - [tavily] D205 not fixable · Issue #1672 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/1672 - [tavily] Multi-root workspace makes Ruff use wrong settings · Issue #925 · astral-sh/ruff-vscode · GitHub — https://github.com/astral-sh/ruff-vscode/issues/925 - [github, open] Feature: Port Sonar's Python scanner checks — https://github.com/astral-sh/ruff/issues/4935 - [tavily] Add check for is comparison with mutable initialisers to rule F632 by jesse1412 · Pull Request #8607 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/pull/8607 - [tavily] [`pyflakes`] Stabilize detection of is comparisons to lists, etc. (`F632`) by charliermarsh · Pull Request #12049 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/pull/12049 - [github, open] Fixes on Jupyter notebooks cause panics when fix replaces/deletes multiple cells — https://github.com/astral-sh/ruff/issues/14445 - [github, open] Implement flake8-async rules — https://github.com/astral-sh/ruff/issues/8451 - [github, open] Suggestion: Implement Sourcery rules — https://github.com/astral-sh/ruff/issues/11060 - [github, closed] B009 safe fix discards evaluation of ** arguments — https://github.com/astral-sh/ruff/issues/28732 - [github, closed] Airflow 3.0 deprecations — https://github.com/astral-sh/ruff/issues/14626 - [github, closed] Implement flake8-type-checking — https://github.com/astral-sh/ruff/issues/1785 - [github, closed] Update bugbear — https://github.com/astral-sh/ruff/issues/2954 - [tavily] 0.16.0 removed 18 rules from the default set without recording it in BREAKING_CHANGES.md · Issue #27199 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/27199 - [tavily] Implement remaining `pycodestyle` rules · Issue #2402 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/2402