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GeezerVison is showing github.com — gh-143732: Specialize `__setitem__` dunder method for `STORE_SUBSCR` by johng · Pull Request #156033 · python/cpython

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@johng

@johng johng commented Aug 19, 2026 •
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This is precursuor for JIT improvements but also results in standard interpreter improvements due to specializing the bytecode.

This improves performance by about 5% on linux and macos micro benchmark

import pyperf


class Grid:
    __slots__ = ("_cell",)

    def __setitem__(self, key, value):
        self._cell = value


def bench_store_subscr(loops):
    obj = Grid()
    range_it = range(loops)
    t0 = pyperf.perf_counter()
    for _ in range_it:
        # 20 stores per loop; keep in sync with inner_loops below
        obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0
        obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0
        obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0
        obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0; obj[0] = 0
    return pyperf.perf_counter() - t0

if __name__ == "__main__":
    runner = pyperf.Runner()
    runner.metadata["description"] = "STORE_SUBSCR on an object with a Python __setitem__"
    runner.bench_time_func("store_subscr_py_dunder", bench_store_subscr, inner_loops=20)
  • Issue: Broader specialization in the Specializing Adaptive Interpreter for better JIT performance #143732

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@bedevere-app bedevere-app Bot mentioned this pull request Aug 19, 2026
Broader specialization in the Specializing Adaptive Interpreter for better JIT performance #143732
Open
@johng
johng force-pushed the gh-143732-store-subscr-py-dunder branch 7 times, most recently from 644baae to 6ccc255 Compare August 19, 2026 02:34
@johng
Specialize __setitem__ dunder method for STORE_SUBSCR
88e57eb
This is precursuor for JIT improvements but also results in
standard improvements due to specializing the bytecode
@johng
johng force-pushed the gh-143732-store-subscr-py-dunder branch from 6ccc255 to 88e57eb Compare August 19, 2026 02:51
@johng
johng marked this pull request as ready for review August 19, 2026 03:01
@johng
johng requested a review from markshannon as a code owner August 19, 2026 03:01
@bedevere-app bedevere-app Bot added the awaiting review label Aug 19, 2026
@markshannon

markshannon commented Aug 19, 2026

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This does not implement the specialization of STORE_SUBSCR for __setitem__ implemented in Python, as described in the issue. If the description in the issue is not clear, please ask for clarification (on the issue, not here)

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@markshannon markshannon added the DO-NOT-MERGE label Aug 19, 2026
@johng

johng commented Aug 20, 2026

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Let me review this in more detail, thanks!

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@johng johng closed this Aug 20, 2026
This was referenced Aug 28, 2026
gh-143732: Specialize __setitem__ dunder method for STORE_SUBSCR johng/cpython#1
Closed
gh-143732: Specialize __setitem__ dunder method for STORE_SUBSCR johng/cpython#2
Closed
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@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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@johng @markshannon
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