[Doc] reimplemented-starmap does not mention performance

[Avasam]

https://github.com/dosisod/refurb/blob/master/docs/checks.md#furb140-use-starmap mentions performance.

https://docs.astral.sh/ruff/rules/reimplemented-starmap/ does not

My local tests seem to agree:

from itertools import starmap
from timeit import timeit

def foo(a: int, b: str): pass

big_list = ["*"] * 99

def test_generator_comprehension():
    return (
        foo(index, value) for index, value
        in enumerate(big_list)
    )

def test_list_comprehension():
    return [
        foo(index, value) for index, value
        in enumerate(big_list)
    ]

def test_generator_starmap():
    return starmap(
        foo,
        enumerate(big_list),
    )

def test_list_starmap():
    return list(
        starmap(
            foo,
            enumerate(big_list),
        ),
    )

print("test_generator_comprehension", timeit(test_generator_comprehension))
print("test_list_comprehension", timeit(test_list_comprehension))
print("test_generator_starmap", timeit(test_generator_starmap))
print("test_list_starmap", timeit(test_list_starmap))

Python 3.9.13:

test_generator_comprehension 0.3537939
test_list_comprehension 9.4948082
test_generator_starmap 0.22116740000000057
test_list_starmap 6.5608599000000005

Python 3.11.2 (surprisingly the generator comprehension is even slower in Python 3.11, despite the proclaimed comprehension speed improvements, list comprehension checks out):

test_generator_comprehension 0.46688559994800016
test_list_comprehension 8.789011800021399
test_generator_starmap 0.24132720002671704
test_list_starmap 7.120547099970281

Scales similarly with a list of ~100 or ~1million items (the list examples takes forever though)

I think it would be important to mention as well. It is not insignificant (a little bit for list, ~2x for generators) and the doc makes it sounds like a simple stylistic change.

[JelleZijlstra]

On Python 3.12 the listcomp is faster (likely thanks to PEP 709). Running @Avasam's benchmark:

test_generator_comprehension 0.19647120800800622
test_list_comprehension 3.4521896250080317
test_generator_starmap 0.15749416704056785
test_list_starmap 3.6789443339803256

(The numbers for generators don't feel very meaningful as it's just for creating the generator, not iterating over it.)

[tjkuson]

I ran the code passing the generators to all to make them actually do things.

On Python 3.11:

test_generator_comprehension 3.9400883330017678
test_generator_starmap 2.439227167000354

On Python 3.12:

test_generator_comprehension 4.032705583002098
test_generator_starmap 3.4624144999979762

So it looks like itertools.starmap is faster for generators, just not comprehensions.

(Accidentally deleted previous comment instead of editing it when trying to correct numbers, apologises for the noise.)