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gh-103000: Optimise dataclasses.asdict for the common case#104364

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AlexWaygood merged 3 commits intopython:mainfrom
AlexWaygood:dataclasses-perf
May 10, 2023
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gh-103000: Optimise dataclasses.asdict for the common case#104364
AlexWaygood merged 3 commits intopython:mainfrom
AlexWaygood:dataclasses-perf

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@AlexWaygood AlexWaygood commented May 10, 2023 •
edited by bedevere-bot
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Now that PEP 709 has been implemented, this change speeds up the following benchmark by 15% on my machine (Windows, PGO-optimised non-debug build):

Benchmark: 
from dataclasses import dataclass, asdict
import timeit

@dataclass
class Foo:
    x: int

@dataclass
class Bar:
    x: Foo
    y: Foo
    z: Foo

@dataclass
class Baz:
    x: Bar
    y: Bar
    z: Bar

foo = Foo(42)
bar = Bar(foo, foo, foo)
baz = Baz(bar, bar, bar)

print(timeit.timeit(lambda: asdict(baz), number=250_000))

This idea was originally @DavidCEllis's, but prior to PEP 709, comprehensions had too much overhead to make it worthwhile. Now that PEP 709 has been implemented, the impact of the patch seems pretty different.

Co-authored-by: David Ellis [email protected]

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@carljm carljm carljm approved these changes

@ericvsmith ericvsmith Awaiting requested review from ericvsmith ericvsmith is a code owner

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@AlexWaygood @carljm @bedevere-bot