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PERF101 false positive #9925

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Skylion007 opened this issue Feb 10, 2024 · 2 comments · Fixed by #9955
Closed

PERF101 false positive #9925

Skylion007 opened this issue Feb 10, 2024 · 2 comments · Fixed by #9955
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@charliermarsh
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@Skylion007
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Skylion007 commented Feb 10, 2024 •
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I was running ruff on Sympy, applied the experimental ruff PERF rules and hit a bug. When running it on this file at this commit:
https://github.com/sympy/sympy/blob/b3d060459054d0cbd925a06fc7719a6f3b498a91/sympy/polys/galoistools.py#L1812 it recommends removing the list cast, but one can't do that because the inner while loop modifies the list that it is iterating over leading to an error. I tried to extract a smaller reproducer out of this, but was unable to.

version used: ruff 0.2.0
ruff --select PERF --show-source --fix file.py leads to the invalid fix.

sympy/polys/galoistools.py:1812:18: PERF101 [*] Do not cast an iterable to `list` before iterating over it
     |
1811 |     for k in range(1, len(V)):
1812 |         for f in list(factors):
     |                  ^^^^^^^^^^^^^ PERF101
1813 |             s = K.zero
     |
     = help: Remove `list()` cast

worse, this is a safe fix and it makes the file invalid.
@Skylion007 Skylion007 changed the title PERF401 false positive PERF101 false positive Feb 10, 2024
@charliermarsh charliermarsh added the bug Something isn't working label Feb 10, 2024
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Makes sense, thanks for filing!

@charliermarsh charliermarsh self-assigned this Feb 11, 2024
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I'll fix this today.

@charliermarsh charliermarsh mentioned this issue Feb 12, 2024
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charliermarsh added a commit that referenced this issue Feb 12, 2024
@charliermarsh
[perflint] Catch a wider range of mutations in PERF101 (#9955)
0304623 
## Summary

This PR ensures that if a list `x` is modified within a `for` loop, we
avoid flagging `list(x)` as unnecessary. Previously, we only detected
calls to exactly `.append`, and they couldn't be nested within other
statements.

Closes #9925.
nkxxll pushed a commit to nkxxll/ruff that referenced this issue Mar 10, 2024
@charliermarsh @nkxxll
[perflint] Catch a wider range of mutations in PERF101 (astral-sh…
5c0a4c7 
…#9955)

## Summary

This PR ensures that if a list `x` is modified within a `for` loop, we
avoid flagging `list(x)` as unnecessary. Previously, we only detected
calls to exactly `.append`, and they couldn't be nested within other
statements.

Closes astral-sh#9925.
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[perflint] Catch a wider range of mutations in PERF101 astral-sh/ruff
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@charliermarsh @Skylion007