[Python-checkins] bpo-34303: Micro-optimizations in functools.reduce() (GH-8598)

[Raymond Hettinger]

https://github.com/python/cpython/commit/e5f6207ba6cb510d9370519ba869296be01787be
commit: e5f6207ba6cb510d9370519ba869296be01787be
branch: master
author: Sergey Fedoseev <fedoseev.sergey at gmail.com>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2019-06-01T13:32:17-07:00
summary:

bpo-34303: Micro-optimizations in functools.reduce() (GH-8598)

files:
A Misc/NEWS.d/next/Library/2018-08-03-09-47-20.bpo-34303.tOE2HP.rst
M Modules/_functoolsmodule.c

diff --git a/Misc/NEWS.d/next/Library/2018-08-03-09-47-20.bpo-34303.tOE2HP.rst b/Misc/NEWS.d/next/Library/2018-08-03-09-47-20.bpo-34303.tOE2HP.rst
new file mode 100644
index 000000000000..94c1299e5956
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-08-03-09-47-20.bpo-34303.tOE2HP.rst
@@ -0,0 +1,2 @@
+Performance of :func:`functools.reduce` is slightly improved. Patch by
+Sergey Fedoseev.
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
index aca5bad23f58..a101363bf02a 100644
--- a/Modules/_functoolsmodule.c
+++ b/Modules/_functoolsmodule.c
@@ -626,10 +626,13 @@ functools_reduce(PyObject *self, PyObject *args)
         if (result == NULL)
             result = op2;
         else {
-            PyTuple_SetItem(args, 0, result);
-            PyTuple_SetItem(args, 1, op2);
-            if ((result = PyEval_CallObject(func, args)) == NULL)
+            /* Update the args tuple in-place */
+            assert(args->ob_refcnt == 1);
+            Py_XSETREF(_PyTuple_ITEMS(args)[0], result);
+            Py_XSETREF(_PyTuple_ITEMS(args)[1], op2);
+            if ((result = PyObject_Call(func, args, NULL)) == NULL) {
                 goto Fail;
+            }
         }
     }