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gh-72902: improve Fraction(str) speed by eendebakpt · Pull Request #149024 · python/cpython · GitHub

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gh-72902: improve Fraction(str) speed - #149024

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eendebakpt wants to merge 4 commits into
python:mainfrom
eendebakpt:fractions_startup
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gh-72902: improve Fraction(str) speed#149024
eendebakpt wants to merge 4 commits into
python:mainfrom
eendebakpt:fractions_startup

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eendebakpt commented Apr 26, 2026 •
edited by bedevere-app Bot
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Improve fractions startup time by improving the regexp and using m.groups(). Added tests have been cherry-picked from #133994 by @skirpichev

Benchmark

Benchmark ref patch
Fraction('123') 1.09 us 902 ns: 1.21x faster
Fraction('1/3') 1.12 us 946 ns: 1.18x faster
Fraction('1.2e-3') 1.66 us 1.29 us: 1.28x faster
Fraction('-.2') 1.38 us 1.05 us: 1.31x faster
Geometric mean (ref) 1.24x faster

with script

import pyperf
from fractions import Fraction as F

runner = pyperf.Runner()
s = 'Fraction'
for v in ["123", "1/3", "1.2e-3", "-.2"]:
    r = s + '(' + repr(v) + ')'
    runner.bench_func(r, F, v)
Detailed changes to the regexp 1. Possessive quantifiers (*+, ++, ?+) — match greedily, never backtrack (digits/underscores can't overlap) 2. `[eE]` instead of `re.IGNORECASE` — only `E` needed case folding 3. `\d*|\d+(_\d+)*` to `(?:\d++(?:_\d++)*+)?+` — same language, no alternation, no backtracking. 4. `/denom` branch unconditional — the other alternation branch already matches empty, so the outer ? was redundant. 5. Drop unnamed capture groups around `(_\d+)*`

(modifications found by Claude, removed a few changes to keep diff shorter)

bedevere-app Bot mentioned this pull request Apr 26, 2026
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skirpichev commented Apr 26, 2026

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PR description looks misleading for me. I guess it's a replacement for #133994.

eendebakpt changed the title gh-72902: Improve fractions startup time gh-72902: improve Fraction(str) speed Apr 27, 2026
eendebakpt mentioned this pull request Aug 6, 2026
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github-actions Bot commented Aug 10, 2026

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This PR is stale because it has been open for 90 days with no activity.

github-actions Bot added the stale Stale PR or inactive for long period of time. label Aug 10, 2026
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