bpo-39028: Performance enhancement in keyword extraction (GH-17576)

All keywords should first be checked for pointer identity. Only after that failed for all keywords (unlikely) should unicode equality be used. The original code would call unicode equality on any non-matching keyword argument. Meaning calling it often e.g. when a function has many kwargs but only the last one is provided.
python · Dec 18, 2019 · 75bb07e92baa7267a61056d03d7e6b475588e793 · 75bb07e
1 parent 50d4f12
commit 75bb07e92baa7267a61056d03d7e6b475588e793
Unified Split

Showing with 8 additions and 3 deletions.

+1 −0 Misc/NEWS.d/next/Core and Builtins/2019-12-17-23-20-51.bpo-39028.SND4TB.rst

+7 −3 Python/getargs.c
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-12-17-23-20-51.bpo-39028.SND4TB.rst b/Misc/NEWS.d/next/Core and Builtins/2019-12-17-23-20-51.bpo-39028.SND4TB.rst
@@ -0,0 +1 @@
+Slightly improve the speed of keyword argument parsing with many kwargs by strengthening the assumption that kwargs are interned strings.
diff --git a/Python/getargs.c b/Python/getargs.c
@@ -2053,14 +2053,18 @@ find_keyword(PyObject *kwnames, PyObject *const *kwstack, PyObject *key)
     Py_ssize_t i, nkwargs;
 
     nkwargs = PyTuple_GET_SIZE(kwnames);
-    for (i=0; i < nkwargs; i++) {
+    for (i = 0; i < nkwargs; i++) {
         PyObject *kwname = PyTuple_GET_ITEM(kwnames, i);
 
-        /* ptr==ptr should match in most cases since keyword keys
-           should be interned strings */
+        /* kwname == key will normally find a match in since keyword keys
+           should be interned strings; if not retry below in a new loop. */
         if (kwname == key) {
             return kwstack[i];
         }
+    }
+
+    for (i = 0; i < nkwargs; i++) {
+        PyObject *kwname = PyTuple_GET_ITEM(kwnames, i);
         assert(PyUnicode_Check(kwname));
         if (_PyUnicode_EQ(kwname, key)) {
             return kwstack[i];