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GeezerVison is showing github.com — Regression in re.compile() performance · Issue #161125 · python/cpython

Regression in re.compile() performance #161125

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Regression in re.compile() performance#161125
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performancePerformance or resource usagePerformance or resource usagestdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

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@eendebakpt
eendebakpt
opened on Nov 1, 2026
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Bug report

The pyperformance regex_compile benchmark is 1.17x slower on main than on 3.15 (1.19x on the free-threaded build). Bisecting points at the gh-152100 series (GH-152153, GH-152154, GH-152214). The regression is also visible on regex_compile on speed.python.org

The reason is redundant work in the case that no fusable constructs are present. Claude has several suggestions, one is in https://github.com/eendebakpt/cpython/tree/re-optimizer-skip-pass.

@serhiy-storchaka

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

  • gh-161125: Avoid redundant work in regex compilation #161600

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  1. eendebakpt
    added
    type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error
    performancePerformance or resource usagePerformance or resource usage
    stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory
    on Nov 1, 2026
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    performancePerformance or resource usagePerformance or resource usagestdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

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