Add C417 - Unnecessary use of map
#409
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Can I also add set comprehensions for |
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I think it makes sense - and I haven't found time to review this properly but it looks good. |
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@adamchainz Merged it all into C417, and added set and dict as well. |
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What is the status on this one? |
README.rst
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| ``map(f, iterable)`` has great performance when ``f`` is a built-in function, | ||
| and it makes sense if your function already has a name. But if you need to | ||
| introduce a lambda, it's more readable and faster to use a generator expression | ||
| or a comprehension -- no function calls needed. |
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I'm tweaking the wording, most notably to remove the readability claim - people love to debate what's readable, but we can be absolutely sure that map is slower 😅
tests/test_flake8_comprehensions.py
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| def test_C417_fail_1(flake8_path): | ||
| (flake8_path / "example.py").write_text( | ||
| dedent( | ||
| """\ | ||
| map(lambda x: x * 2, iterable) | ||
| list(map(lambda x: x * 2, iterable)) | ||
| set(map(lambda num: num % 2 == 0, nums)) | ||
| dict(map(lambda v: (v, v ** 2), values)) | ||
| """ | ||
| ) | ||
| ) | ||
| result = flake8_path.run_flake8() | ||
| assert result.out_lines == [ | ||
| "./example.py:1:1: C417 Unnecessary use of map - " | ||
| "use a generator expression instead.", | ||
| "./example.py:2:1: C417 Unnecessary use of map - " | ||
| "use a list comprehension instead.", | ||
| "./example.py:3:1: C417 Unnecessary use of map - " | ||
| "use a set comprehension instead.", | ||
| "./example.py:4:1: C417 Unnecessary use of map - " | ||
| "use a dict comprehension instead.", | ||
| ] |
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I will split this test - I deliberately want separate test cases so it's easy to see what fails/passes whilst editing code.
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Released in 3.10.0, thanks! |
Resolves #405