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gh-154675: Avoid importing inspect when creating a slotted dataclass - #156841

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python:mainfrom
aisk:dataclasses-inline-unwrap
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gh-154675: Avoid importing inspect when creating a slotted dataclass#156841
aisk wants to merge 2 commits into
python:mainfrom
aisk:dataclasses-inline-unwrap

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@aisk

@aisk aisk commented Sep 2, 2026 •
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Using @dataclass(slots=True) always imports inspect, just for the single inspect.unwrap() call in _add_slots().

typing and annotationlib already inline the same __wrapped__ walk to avoid the import, so dataclasses can too. Perhaps in the future unwrap() could move into a small private module that inspect and all these copies import, so the implementations do not drift apart.

Importing a module that defines one slotted dataclass, best of 30 runs.

$ cat app.py
from dataclasses import dataclass

@dataclass(slots=True)
class Point:
    x: int = 0
    y: int = 0

$ ./python -c 'import time; t = time.perf_counter(); import app; print(time.perf_counter() - t)'
0.022856871997646522   # before
0.010011243997723795   # after

About 2.3x faster.

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aisk requested a review from ericvsmith as a code owner September 2, 2026 16:48
@bedevere-app bedevere-app Bot mentioned this pull request Sep 2, 2026
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@eendebakpt

eendebakpt commented Sep 9, 2026

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typing and annotationlib already inline the same __wrapped__ walk to avoid the import, so dataclasses can too. Perhaps in the future unwrap() could move into a small private module that inspect and all these copies import, so the implementations do not drift apart.

Adding another copy to be kept in sync is not very appealing, so I would be in favor of checking whether the private module idea can work. (note that typing and annotationlib use a set for the memo instead of a dict, which can potentially lead to issues when ids are reused).

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@aisk @eendebakpt