gh-137855: Optimise import time for textwrap

[AA-Turner]

This uses self-overwriting descriptors to implement compiled class-level patterns. An unorthodox approach, but I think cleaner than using is None checks everywhere. If this looks reasonable, I'll add NEWS etc.

A

• Issue: Improve import time of various stdlib modules #118761

• Issue: Improve import time of various stdlib modules #137855

[picnixz]

That's an interesting and cleaner way to make it work but maybe we could add some tests as well, just in case?

[AA-Turner]

we could add some tests as well, just in case?

Happy to, do you mean for _cached_regex, or tests for TextWrapper, or?

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[picnixz]

I think tests with accessing / resetting / deleting the attributes (they are publicly named even though they are not exposed, just in case someone is subclassing them [again they shouldn't be part of the public API but well.. you never know; and it would be good to just check that the patterns are the expected ones.

But yes, also a small test for the descriptor with a fake pattern and check that its implementation is correct (well it should be AFAIK).

[vstinner]

I'm not excited by this change, IMO it goes too far :-(

This change is an optimization, you should provide a benchmark to prove that the change is worth it.

[AA-Turner]

This change is an optimization, you should provide a benchmark to prove that the change is worth it.

@vstinner sorry for not including them. Benchmarks show a consistent large decrease in import time, around 10ms on a standard release build in Windows. See below for detailed numbers:

Using -X importtime -Sc 'import textwrap'

Old: import time: 907 | 10796 | textwrap_current
New: import time: 311 | 311 | textwrap_new

The same command, on the default PCbuild\build.bat build:

Old: import time: 5272 | 29988 | textwrap_current
New: import time: 1076 | 1076 | textwrap_new

With hyperfine, Python 3.13.2:

PS> hyperfine -N --warmup 5 "python -c ''" "python -c 'import textwrap_current'" "python -c 'import textwrap_new'" Benchmark 1: python -c '' Time (mean ± σ): 24.1 ms ± 0.9 ms [User: 5.4 ms, System: 3.4 ms] Range (min … max): 22.3 ms … 26.4 ms 124 runs Benchmark 2: python -c 'import textwrap_current' Time (mean ± σ): 34.6 ms ± 1.5 ms [User: 8.3 ms, System: 4.0 ms] Range (min … max): 29.5 ms … 38.1 ms 85 runs Benchmark 3: python -c 'import textwrap_new' Time (mean ± σ): 24.2 ms ± 0.9 ms [User: 8.3 ms, System: 3.7 ms] Range (min … max): 21.8 ms … 27.0 ms 124 runs 

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[python-cla-bot]

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