diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-05-17-12-00-00.gh-issue-138325.h2XSfe.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-17-12-00-00.gh-issue-138325.h2XSfe.rst new file mode 100644 index 00000000000000..0eb528c68d8d6f --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-17-12-00-00.gh-issue-138325.h2XSfe.rst @@ -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. diff --git a/Python/intrinsics.c b/Python/intrinsics.c index 9cfc285c6a5925..9f994950f2721d 100644 --- a/Python/intrinsics.c +++ b/Python/intrinsics.c @@ -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() @@ -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 *