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gh-138912: Improve MATCH_CLASS opcode performance - #138915

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gpshead merged 15 commits into
python:mainfrom
cdce8p:match-class-performance
Feb 14, 2026
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gh-138912: Improve MATCH_CLASS opcode performance#138915
gpshead merged 15 commits into
python:mainfrom
cdce8p:match-class-performance

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@cdce8p

@cdce8pcdce8p commented Sep 15, 2025•
edited by bedevere-app Bot
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cdce8p
cdce8p commented Sep 15, 2025
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Comment threadPython/ceval.c Outdated
if (seen == NULL) {
return NULL;
PyObject *seen = NULL;
if (nattrs > 1) {

@cdce8pcdce8pSep 15, 2025

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Suggested change
if (nattrs>1) {
if (nargs>1|| (nargs==1&&nkwargs>0)) {

As mentioned in #138912, I'd also like to change this. If there are only keyword arguments, it's easy to see if two are the same name. Furthermore linters are able to detect these based on the AST alone.

It would also be great to say if we could suggest users to prefer keyword arguments. Not only are they more explicit, they are also faster. (No lookup of __match_args__ and, with the change, no expensive duplicate name detection.)

@cdce8pcdce8pSep 15, 2025

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Added this in f585253 with if (nargs > 0 && nattrs > 1). I can revert it if necessary.

@cdce8pcdce8pDec 21, 2025•
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Only mentioned it on the issue a while ago but the keyword attributes are validated already during the compile stage at which point a SyntaxError is raised. Just added an explicit test case for it in 9375e2b.

sergey-miryanov
sergey-miryanov reviewed Sep 15, 2025
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Comment threadPython/ceval.c
ZeroIntensity
ZeroIntensity reviewed Sep 16, 2025
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Comment threadPython/ceval.c Outdated
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Comment threadMisc/NEWS.d/next/Core_and_Builtins/2025-09-15-13-28-48.gh-issue-138912.61EYbn.rst Outdated
@cdce8pcdce8p mentioned this pull request Sep 17, 2025
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eendebakpt
eendebakpt approved these changes Oct 28, 2025
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Comment threadPython/ceval.c Outdated
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eendebakpt commented Nov 11, 2025

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The CI failure seems unrelated. Updating the branch to rerun the CI just to be sure.

@cdce8p
cdce8pforce-pushed the match-class-performance branch from 359df88 to e0c2c1eCompareNovember 20, 2025 10:39
sergey-miryanov
sergey-miryanov approved these changes Jan 24, 2026
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LGTM

gpshead
gpshead approved these changes Feb 14, 2026
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nice!

@gpsheadgpshead added the performance Performance or resource usage label Feb 14, 2026
@gpshead
gpshead merged commit 75d4839 into python:mainFeb 14, 2026
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@cdce8p
cdce8p deleted the match-class-performance branch February 14, 2026 09:59
@cdce8p

cdce8p commented Feb 14, 2026

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Thanks for the review @gpshead. Is this change something which could be backported to 3.14 and maybe 3.13? Would be great to not have to wait until 3.15 for the performance improvements here.

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gpshead commented Feb 16, 2026

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Sorry, we only backport bugfixes and documentation updates.

@cdce8pcdce8p mentioned this pull request Feb 27, 2026
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brijkapadia pushed a commit to brijkapadia/cpython that referenced this pull request Feb 28, 2026
@cdce8p@brijkapadia
pythongh-138912: Improve MATCH_CLASS opcode performance (pythonGH-138915
a12a0e0
)
Only check for duplicates if there is at least one positional pattern.
With a test case for duplicate keyword attributes.
ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@cdce8p@ljfp
pythongh-138912: Improve MATCH_CLASS opcode performance (pythonGH-138915
19e3278
)
Only check for duplicates if there is at least one positional pattern.
With a test case for duplicate keyword attributes.
@eendebakpteendebakpt mentioned this pull request Apr 28, 2026
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@sergey-miryanovsergey-miryanovsergey-miryanov approved these changes
@gpsheadgpsheadgpshead approved these changes
@eendebakpteendebakpteendebakpt approved these changes
@markshannonmarkshannonAwaiting requested review from markshannonmarkshannon is a code owner
@ZeroIntensityZeroIntensityAwaiting requested review from ZeroIntensity

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