gh-137855: Improve import time of dataclasses by lazy importing re and copy modules#148379
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danielhollas wants to merge 7 commits intopython:mainfrom
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gh-137855: Improve import time of dataclasses by lazy importing re and copy modules#148379danielhollas wants to merge 7 commits intopython:mainfrom
re and copy modules#148379danielhollas wants to merge 7 commits intopython:mainfrom
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hugovk
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Apr 11, 2026
Lib/dataclasses.py
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| global _MODULE_IDENTIFIER_RE | ||
| if _MODULE_IDENTIFIER_RE is None: | ||
| _MODULE_IDENTIFIER_RE = re.compile(r'^(?:\s*(\w+)\s*\.)?\s*(\w+)') | ||
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| match = _MODULE_IDENTIFIER_RE.match(annotation) |
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Oh look, the regex starts with a ^ anchor, but then uses match, which is now better expressed with its prefixmatch alias:
https://docs.python.org/3.15/library/re.html#prefixmatch-vs-match
Let's either use search with ^, or prefixmatch without ^.
And a micro-optimisation for below, match[x] (introduced in 3.6) is a bit faster than match.group(x).
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Cool! I went with prefixmatch
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There's also a match.group(2) on line 826.
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Ah, good catch, sorry about that
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
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The failing Ubuntu build is a transient issue during dependency installation that will hopefully go away when the job is restarted. |
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Split from #144387 as requested by @hugovk (tagging for review :-) This is a relatively minor win, the bigger win will come from lazy importing inspect in #144387
See below for tuna-visualized outputs from
./python -X importtime -c "import dataclasses"(the absolute import numbers are not representative as I was running a debug python build)
Before
After