https://github.com/python/cpython/commit/6999d68d2878871493d85dc63599f3d44eada104
commit: 6999d68d2878871493d85dc63599f3d44eada104
branch: main
author: Shantanu <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2024-04-30T23:16:52+03:00
summary:
gh-118218: Reuse return tuple in itertools.pairwise (GH-118219)
files:
A Misc/NEWS.d/next/Library/2024-04-24-07-45-08.gh-issue-118218.m1OHbN.rst
M Lib/test/test_itertools.py
M Modules/itertoolsmodule.c
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 95e67911db6a7f..e243da309f03d8 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -1821,6 +1821,13 @@ def test_zip_longest_result_gc(self):
gc.collect()
self.assertTrue(gc.is_tracked(next(it)))
+ @support.cpython_only
+ def test_pairwise_result_gc(self):
+ # Ditto for pairwise.
+ it = pairwise([None, None])
+ gc.collect()
+ self.assertTrue(gc.is_tracked(next(it)))
+
@support.cpython_only
def test_immutable_types(self):
from itertools import _grouper, _tee, _tee_dataobject
diff --git
a/Misc/NEWS.d/next/Library/2024-04-24-07-45-08.gh-issue-118218.m1OHbN.rst
b/Misc/NEWS.d/next/Library/2024-04-24-07-45-08.gh-issue-118218.m1OHbN.rst
new file mode 100644
index 00000000000000..6d3c54cb485655
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-04-24-07-45-08.gh-issue-118218.m1OHbN.rst
@@ -0,0 +1 @@
+Speed up :func:`itertools.pairwise` in the common case by up to 1.8x.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 6ee447ef6a8cd6..21ce3ecfad0354 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -270,6 +270,7 @@ typedef struct {
PyObject_HEAD
PyObject *it;
PyObject *old;
+ PyObject *result;
} pairwiseobject;
/*[clinic input]
@@ -301,6 +302,11 @@ pairwise_new_impl(PyTypeObject *type, PyObject *iterable)
}
po->it = it;
po->old = NULL;
+ po->result = PyTuple_Pack(2, Py_None, Py_None);
+ if (po->result == NULL) {
+ Py_DECREF(po);
+ return NULL;
+ }
return (PyObject *)po;
}
@@ -311,6 +317,7 @@ pairwise_dealloc(pairwiseobject *po)
PyObject_GC_UnTrack(po);
Py_XDECREF(po->it);
Py_XDECREF(po->old);
+ Py_XDECREF(po->result);
tp->tp_free(po);
Py_DECREF(tp);
}
@@ -321,6 +328,7 @@ pairwise_traverse(pairwiseobject *po, visitproc visit, void
*arg)
Py_VISIT(Py_TYPE(po));
Py_VISIT(po->it);
Py_VISIT(po->old);
+ Py_VISIT(po->result);
return 0;
}
@@ -355,8 +363,30 @@ pairwise_next(pairwiseobject *po)
Py_DECREF(old);
return NULL;
}
- /* Future optimization: Reuse the result tuple as we do in enumerate() */
- result = PyTuple_Pack(2, old, new);
+
+ result = po->result;
+ if (Py_REFCNT(result) == 1) {
+ Py_INCREF(result);
+ PyObject *last_old = PyTuple_GET_ITEM(result, 0);
+ PyObject *last_new = PyTuple_GET_ITEM(result, 1);
+ PyTuple_SET_ITEM(result, 0, Py_NewRef(old));
+ PyTuple_SET_ITEM(result, 1, Py_NewRef(new));
+ Py_DECREF(last_old);
+ Py_DECREF(last_new);
+ // bpo-42536: The GC may have untracked this result tuple. Since we're
+ // recycling it, make sure it's tracked again:
+ if (!_PyObject_GC_IS_TRACKED(result)) {
+ _PyObject_GC_TRACK(result);
+ }
+ }
+ else {
+ result = PyTuple_New(2);
+ if (result != NULL) {
+ PyTuple_SET_ITEM(result, 0, Py_NewRef(old));
+ PyTuple_SET_ITEM(result, 1, Py_NewRef(new));
+ }
+ }
+
Py_XSETREF(po->old, new);
Py_DECREF(old);
return result;
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