Ignore Ruff RUF015

[autinerd]

Proposed change

EDIT: This ignores the Ruff rule RUF015.

ORIGINAL:

This enables the Ruff rule RUF015: Prefer next(...) over single element slice.

This performs two transformations:

1. list(x)[0] --> next(iter(x))
2. [x for x in y][0] --> next(x for x in y)

Using next for 1. is quite a bit faster (of course depends on the size of the object):

❯ python3 -m timeit 'list({"1": "a", "e": 23})[0]'
1000000 loops, best of 5: 297 nsec per loop
❯ python3 -m timeit 'next(iter({"1": "a", "e": 23}))'
2000000 loops, best of 5: 194 nsec per loop

For 2., next is actually slower if the source list contains only a few elements:

❯ python3 -m timeit '[i for i in [1,2,3,4,5]][0]'
1000000 loops, best of 5: 354 nsec per loop
❯ python3 -m timeit 'next(i for i in [1,2,3,4,5])'
500000 loops, best of 5: 496 nsec per loop

But from about 14 elements onwards (on my machine), next is faster:

❯ python3 -m timeit '[i for i in [1,2,3,4,5,6,7,8,9,0,1,2,3,4]][0]'
500000 loops, best of 5: 496 nsec per loop
❯ python3 -m timeit 'next(i for i in [1,2,3,4,5,6,7,8,9,0,1,2,3,4])'
500000 loops, best of 5: 486 nsec per loop

(When the generator expression / list comprehension contains an if clause for filtering, next gets already faster with fewer elements)

❯ python3 -m timeit '[i for i in [1,2,3,4,5,6,7,8,9,0,1,2,3,4] if i % 2 == 0][0]'
500000 loops, best of 5: 844 nsec per loop
❯ python3 -m timeit 'next(i for i in [1,2,3,4,5,6,7,8,9,0,1,2,3,4] if i % 2 == 0)'
500000 loops, best of 5: 570 nsec per loop

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

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• Tests have been added to verify that the new code works.

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[puddly]

If x is a generator, this will change behavior by not exhaustively iterating over the whole thing (which only matters if the generator has side effects). Not sure if it matters here though, none of the code I'm able to spot does this.

[autinerd]

Yes of course, it is short-circuting, but I didn't see anything as well which should be impacted by it.

[cdce8p]

I'm not sure we should really do that. Of course next might be slightly faster but in most of these cases that doesn't really matter all that much. The more important thing IMO is that, especially for beginners, wrapping something with list and accessing the first element is easier to reason about than next(...).

If it makes sense in a specific case, e.g. because it's part of the core and often executed, I'm not against using next but I would suggest we don't enable this rule.

[autinerd]

Okay, then I revert the changes and put it on ignore instead.

[cdce8p]

Thanks @autinerd 👍🏻