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gh-138325: steal list items in INTRINSIC_LIST_TO_TUPLE #149960

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Merged
kumaraditya303 merged 1 commit into from
May 18, 2026
+11 −2
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gh-138325: steal list items in INTRINSIC_LIST_TO_TUPLE #149960

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-05-17-12-00-00.gh-issue-138325.h2XSfe.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Speed up converting a list to a tuple in the ``tuple(genexpr)`` fast path
and in starred tuple displays (e.g. ``(*a, *b)``) by stealing the list's
items into the tuple instead of copying them.
10 changes: 8 additions & 2 deletions Python/intrinsics.c
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Expand Up @@ -7,6 +7,8 @@
#include "pycore_genobject.h" // _PyAsyncGenValueWrapperNew
#include "pycore_interpframe.h" // _PyFrame_GetLocals()
#include "pycore_intrinsics.h" // INTRINSIC_PRINT
#include "pycore_list.h" // _PyList_AsTupleAndClear()
#include "pycore_object.h" // _PyObject_IsUniquelyReferenced()
#include "pycore_pyerrors.h" // _PyErr_SetString()
#include "pycore_runtime.h" // _Py_ID()
#include "pycore_typevarobject.h" // _Py_make_typevar()
Expand Down Expand Up @@ -190,8 +192,12 @@ unary_pos(PyThreadState* unused, PyObject *value)
static PyObject *
list_to_tuple(PyThreadState* unused, PyObject *v)
{
assert(PyList_Check(v));
return PyTuple_FromArray(((PyListObject *)v)->ob_item, Py_SIZE(v));
/* INTRINSIC_LIST_TO_TUPLE is only emitted by the compiler for a
freshly-built, uniquely-referenced temporary list, so steal its items
into the tuple instead of copying them. */
assert(PyList_CheckExact(v));
assert(_PyObject_IsUniquelyReferenced(v));
return _PyList_AsTupleAndClear((PyListObject *)v);
}

static PyObject *
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