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gh-145192: Improve performance of PySequence_GetSlice #145193

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gh-145192: Improve performance of PySequence_GetSlice #145193

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569002d
Avoid reference counts on pyslice_fromindices
eendebakpt Feb 19, 2026
66c1209
avoid incref on step argument
eendebakpt Feb 19, 2026
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Merge branch 'main' into pyslice_fromindices
eendebakpt Feb 24, 2026
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Merge branch 'main' into pyslice_fromindices
eendebakpt Mar 26, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/C_API/2026-02-24-20-07-41.gh-issue-145192.Td5zue.rst
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@@ -0,0 +1 @@
Improve performance of :c:func:`PySequence_GetSlice`.
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15 changes: 7 additions & 8 deletions Objects/sliceobject.c
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Expand Up @@ -118,7 +118,7 @@ PyObject _Py_EllipsisObject = _PyObject_HEAD_INIT(&PyEllipsis_Type);
*/

static PySliceObject *
_PyBuildSlice_Consume2(PyObject *start, PyObject *stop, PyObject *step)
_PyBuildSlice_Consume3(PyObject *start, PyObject *stop, PyObject *step)
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@markshannon markshannon Feb 26, 2026

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Since this consumes all its argument references, the 3 is unnecessary

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@markshannon markshannon Feb 26, 2026

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In fact, this is now the same as _PyBuildSlice_ConsumeRefs, so you can rename this function and delete the other definition of _PyBuildSlice_ConsumeRefs

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@eendebakpt eendebakpt Feb 26, 2026 •
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The _PyBuildSlice_ConsumeRefs only takes 2 arguments. I can delete it, but it would involve some churn (e.g. in bytecodes.c) because we have to add Py_None as a third argument.

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@eendebakpt eendebakpt Feb 26, 2026

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@markshannon I merged the two methods!

{
assert(start != NULL && stop != NULL && step != NULL);
PySliceObject *obj = _Py_FREELIST_POP(PySliceObject, slices);
Expand All @@ -131,13 +131,14 @@ _PyBuildSlice_Consume2(PyObject *start, PyObject *stop, PyObject *step)

obj->start = start;
obj->stop = stop;
obj->step = Py_NewRef(step);
obj->step = step;

_PyObject_GC_TRACK(obj);
return obj;
error:
Py_DECREF(start);
Py_DECREF(stop);
Py_DECREF(step);
return NULL;
}

Expand All @@ -153,15 +154,15 @@ PySlice_New(PyObject *start, PyObject *stop, PyObject *step)
if (stop == NULL) {
stop = Py_None;
}
return (PyObject *)_PyBuildSlice_Consume2(Py_NewRef(start),
Py_NewRef(stop), step);
return (PyObject *)_PyBuildSlice_Consume3(Py_NewRef(start),
Py_NewRef(stop), Py_NewRef(step));
}

PyObject *
_PyBuildSlice_ConsumeRefs(PyObject *start, PyObject *stop)
{
assert(start != NULL && stop != NULL);
return (PyObject *)_PyBuildSlice_Consume2(start, stop, Py_None);
return (PyObject *)_PyBuildSlice_Consume3(start, stop, Py_None);
}

PyObject *
Expand All @@ -177,9 +178,7 @@ _PySlice_FromIndices(Py_ssize_t istart, Py_ssize_t istop)
return NULL;
}

slice = PySlice_New(start, end, NULL);
Py_DECREF(start);
Py_DECREF(end);
slice = _PyBuildSlice_ConsumeRefs(start, end);
return slice;
}

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