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base repository: python/cpython
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head repository: eendebakpt/cpython
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compare: match-class-perf
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  • 1 commit
  • 3 files changed
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Commits on Jun 29, 2026

  1. Speed up zero-argument class patterns in match statements 

    A class pattern with no sub-patterns (`case C():`) is just an isinstance
check, but it compiled to LOAD_COMMON_CONSTANT (empty names tuple) +
MATCH_CLASS + COPY + POP_JUMP_IF_NONE + UNPACK_SEQUENCE 0, building and
unpacking an empty attributes tuple every time.

Compile it instead to a CALL_INTRINSIC_2 invoking a new
INTRINSIC_MATCH_CLASS_ISINSTANCE, which performs the same PyType_Check
and PyObject_IsInstance as _PyEval_MatchClass (including the identical
TypeError when the pattern does not name a class) and pushes a bool.
No new opcode is added.

This is ~25% faster on a matching subject and ~14% faster on a
non-matching subject for the zero-argument case, and is even faster than
an equivalent isinstance() call since the intrinsic avoids a Python-level
call frame.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
    @eendebakpt @claude
    eendebakpt and claude committed Jun 29, 2026
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