improve error message of PERF401 for extends

[trim21]

import os
from pathlib import Path
from typing import Any


directory: Any = []

files: list[Path] = []
for p in directory:
    if p.is_file():
        files.append(p)
    else:
        for dir, _, _files in os.walk(p):
            for _f in _files:
                files.append(Path(dir).joinpath(_f)) # PERF401 Use a list comprehension to create a transformed list

https://play.ruff.rs/cde69c3f-1d15-4089-bb62-5de79566898a

ruff version 0.4.1

(Is this even possible to re-write with list comprehension?)

[JonathanPlasse]

You can rewrite it like this. Only the inner for loops need to be rewritten.

import os
from pathlib import Path
from typing import Any


directory: Any = []

files: list[Path] = []
for p in directory:
    if p.is_file():
        files.append(p)
    else:
        files.extend(
            Path(dir).joinpath(_f) for dir, _, _files in os.walk(p) for _f in _files
        )

[trim21]

You can rewrite it like this. Only the inner for loops need to be rewritten.

import os
from pathlib import Path
from typing import Any


directory: Any = []

files: list[Path] = []
for p in directory:
    if p.is_file():
        files.append(p)
    else:
        files.extend(
            Path(dir).joinpath(_f) for dir, _, _files in os.walk(p) for _f in _files
        )

so the problem is error message not very clear…

[JonathanPlasse]

Indeed

[trim21]

I'm not a fan of nested loop in list comprehension repr, I would just disable this rule and leave this issue open...

[JonathanPlasse]

The documentation does precise that .extend can be used for existing lists.

[charliermarsh]

I think this is actually okay because it is included in the documentation, and it would be hard to know whether or not to recommend this in the error message itself.