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GeezerVison is showing github.com — Increase speed of Fractions.limit_denominator · Issue #93476 · python/cpython

Increase speed of Fractions.limit_denominator #93476

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Increase speed of Fractions.limit_denominator#93476
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3.12only security fixesonly security fixesperformancePerformance or resource usagePerformance or resource usagestdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directorytype-featureA feature request or enhancementA feature request or enhancement

Description

@mscuthbert
mscuthbert
opened on Jun 3, 2022
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Feature or enhancement

Speed up Fractions.limit_denominator by not creating intermediary Fraction objects

Pitch

Fractions.limit_denominator returns a new Fraction, but along the way for Fractions > max_denominator creates 3 Fraction objects that are discarded: the fraction farther from the bound and two temporary fractions (bound1 - self and bound2 - shelf) which are created just for getting their absolute values.

Similar code speedups have been part of the music21 library since 2015--where we call limit_denominator after every arithmetic operation on note placement--and timing tests give a 7.3x speedup. (see music21 Source )

For fractions with denominators equal to or below max_denominator, instantiate the new Fraction with Fraction(self._numerator, self._denominator) instead of Fraction(self) for a 23% speedup.

PR to follow.

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  1. mscuthbert
    added
    type-featureA feature request or enhancementA feature request or enhancement
    on Jun 3, 2022
  2. mscuthbert
    added a commit that references this issue on Jun 3, 2022

    pythongh-93476: Fraction.limit_denominator speed increases

    599c55b
  3. AlexWaygood
    added
    performancePerformance or resource usagePerformance or resource usage
    stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory
    3.12only security fixesonly security fixes
    on Jun 3, 2022

  4. rhettinger commented on Jun 5, 2022

    @rhettinger
    rhettinger
    on Jun 5, 2022
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    In this case, we value algorithmic clarity over a minor performance gain from inlining.

    Also, we would lose some of the recent optimizations in the Fraction class.

    The limit_denominator code is almost never in a performance critical section of code, so no one would notice the small benefit, but we would incur a loss of understanding about how it works.

    Thanks for the suggestion, but we will decline this one.

  5. rhettinger
    closed this as completedon Jun 5, 2022
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