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[flake8-simplify] SIM109 fix reorders statements incorrectly #18945
Description
Summary
I found this while working on #15584
compare-with-tuple (SIM109) does not respect the or ordering in expressions. x or y == z or y == w should be turned into x or (y in (z, w)), but instead becomes y in (z, w) or x, changing the meaning of the code.
https://play.ruff.rs/f7ed8e28-c451-48d8-ace1-c1fdb85f51cd
PS ~\Desktop\New_folder\ruff>Get-Content issue.py
x = None
y = "y"
z = "z"
w = "w"
print(x or y == z or y == w)PS ~\Desktop\New_folder\ruff>py issue.py
False
PS ~\Desktop\New_folder\ruff>uvx ruff check issue.py --isolated --select SIM
issue.py:5:7: SIM109 Use `y in (z, w)` instead of multiple equality comparisons
|
3 | z = "z"
4 | w = "w"
5 | print(x or y == z or y == w)
| ^^^^^^^^^^^^^^^^^^^^^ SIM109
|
= help: Replace with `y in (z, w)`
Found 1 error.
No fixes available (1 hidden fix can be enabled with the `--unsafe-fixes` option).PS ~\Desktop\New_folder\ruff>uvx ruff check issue.py --isolated --select SIM --fix --unsafe-fixes
Found 1 error (1 fixed, 0 remaining).
PS ~\Desktop\New_folder\ruff>Get-Content issue.py
x = None
y = "y"
z = "z"
w = "w"
print(y in (z, w) or x)PS ~\Desktop\New_folder\ruff>py issue.py
None
Other misc things about SIM109 I noticed:
The lint currently doesn't apply at all if there are comments inside the expr, but I don't know why. I think it should instead be a normally safe fix, and only unsafe if there are comments. (There is the same amount of __eq__ calls pre and post fix, ordering in those calls is preserved, and the code already doesn't lint if there is any possibility of other side effects.)
Version
ruff 0.12.0 (87f0feb 2025-06-17) + playground
Activity
[-][`flake8-simplify`] `SIM109` does not respect `or` ordering (false positive)[/-][+][`flake8-simplify`] `SIM109` fix reorders statements incorrectly[/+]ntBre commentedon Jun 25, 2025
Thanks, this seems like a bug. Maybe we can use
OperatorPrecedencehere.With regard to the fix, I'm not sure if we want to upgrade it to a safe fix when there are no comments, but we could at least avoid the
continuein the presence of comments since it's already unsafe.mikeleppane commentedon Aug 5, 2025
I'm working on this.
[flake8-simplify] Preserve operand order in SIM109 fix (#27824)