Improve performance of asdict in the common case

[eendebakpt]

Summary

We improve performance of attrs.asdict by:

• Using a fast check for atomic types (list int, float or str)
• Using issubclass instead of isinstance for various type checks

Benchmark:

asdict: Mean +- std dev: [main] 4.07 us +- 0.41 us -> [pr] 2.48 us +- 0.21 us: 1.64x faster

Benchmark hidden because not significant (1): instance creation

Geometric mean: 1.28x faster

Test script

import pyperf

setup = """
from attrs import define, asdict

@define
class Simple:
     i : int
     s : str
     l : list

s = Simple(10, 'hi', [3, 1, 4])

"""

runner = pyperf.Runner()
runner.timeit(name="instance creation", stmt="Simple(10, 'hi', [3, 1, 4])", setup=setup)
runner.timeit(name="asdict", stmt="asdict(s)", setup=setup)

Notes:

• a similar PR was added to cpython dataclasses as well gh-103000: Optimise dataclasses asdict/astuple for common types python/cpython#103005
• With a similar approach we can improve performance of astuple. That is left to a separate PR though. Also see attrs.astuple() leaves performance on the table compared to operator.attrgetter #1129

Pull Request Check List

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• Added tests for changed code.
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• New features have been added to our Hypothesis testing strategy.
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  • ...and used in the stub test file tests/typing_example.py.
  • If they've been added to attr/__init__.pyi, they've also been re-imported in attrs/__init__.pyi.
• Updated documentation for changed code.
  • New functions/classes have to be added to docs/api.rst by hand.
  • Changes to the signatures of @attr.s() and @attrs.define() have to be added by hand too.
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[codspeed-hq]

CodSpeed Performance Report

Merging #1463 will improve performances by ×2.6

_{Comparing eendebakpt:asdict_atomic_types (080dbc5) with main (5d216e6)¹}

Summary

⚡ 2 improvements
✅ 10 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	test_asdict_atomic	16.3 ms	6.4 ms	×2.6
⚡	test_asdict_complicated	13.8 ms	9.5 ms	+45.6%

Footnotes

1. No successful run was found on main (57f0d54) during the generation of this report, so 5d216e6 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[hynek]

Thanks!