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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
3b09eec
Merge branch 'main' into pyslice_fromindices
eendebakpt Feb 24, 2026
d7b0367
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 24, 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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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Improve performance of :c:func:`PySequence_GetSlice`.
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@benediktjohannes benediktjohannes Feb 24, 2026

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The Change Looks really good to me, thank You for fixing this!

I only suggest going a Bit more in Detail for the Description, but very nice fix!

LGTM!

Suggested change
Improve performance of :c:func:`PySequence_GetSlice`.
Improve performance of :c:func:`PySequence_GetSlice` by avoiding unnecessary reference count decrements.

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)
{
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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