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gh-157407: Shrink _PyArg_Parser and don't write builtin parsers at run time - #157531
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…cally Argument Clinic now sets _PyArg_Parser.pos statically. Parsers with a statically allocated keyword tuple (builtin modules) therefore need no initialization: _PyArg_UnpackKeywords() skips parser_init() for them, so they are never written to at run time. A lazily built keyword tuple is now published last, with _Py_atomic_store_ptr_release(). parser_clear() keeps pos, since it only depends on the keywords. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Narrow pos, min, max and is_kwtuple_owned, which are small counts, and remove custom_msg: it is only needed to report a conversion error, and can then be looked up in the format string. Keep format, keywords and fname first, so that existing positional initializers still work. _PyArg_Parser shrinks from 72 to 48 bytes on 64-bit platforms. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
eendebakpt
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ericsnowcurrently and
erlend-aasland
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September 14, 2026 21:57
maurycy
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Sep 15, 2026
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Make the argument clinic generated code more efficient:
.pos = Nin the static_PyArg_Parserwith allows_PyArg_UnpackKeywords()to skipparser_init()._PyArg_Parser.pos/min/maxbecomeuint16_tandis_kwtuple_ownedbecomesuint8_t.custom_msgis removed: it is only needed when reporting a conversion error, so it is now looked up in the format string (";message") on that path. No in-tree parser uses";message"._parser_init()raisesSystemErrorfor more than 65535 keywords. The struct goes from 73 bytes to 48 bytes.Binary size change:
.data/ file size, main vs. this PR (Release builds):python316.dll(MSVC)*.pyd+ dllpython(gcc 15, static libpython)python+ all*.soPossible follow-ups
With some more refactoring this could go further:
format,minormax. Builtin-module parsers also never useonce,is_kwtuple_ownedornext. A separate, smaller struct for them would save more memory, at the cost of changing the private API.fname,minandmaxfor format-string parsers, so that builtin ones skipparser_init()too.parser_clear()then only needs to reset the kwtuple andonce, since the other fields only depend on the static keywords and format.Generated with help from Claude Code