SF patch #1200051: Small optimization for PyDict_Merge()

(Contributed by Barry Warsaw and Matt Messier.)

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 1be34774e3e365b35f05f4840f9e01432c7990fe..aaca5aa4c1dae36d91336fb75b759bef72bb5b95 100644 (file)
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -1203,6 +1203,12 @@ PyDict_Merge(PyObject *a, PyObject *b, int override)
                if (other == mp || other->ma_used == 0)
                        /* a.update(a) or a.update({}); nothing to do */
                        return 0;
+               if (mp->ma_used == 0)
+                       /* Since the target dict is empty, PyDict_GetItem()
+                        * always returns NULL.  Setting override to 1
+                        * skips the unnecessary test.
+                        */
+                       override = 1;
                /* Do one big resize at the start, rather than
                 * incrementally resizing as we insert new items.  Expect
                 * that there will be no (or few) overlapping keys.