From 8725dce2ae77aeac72cdfa024a1d0aff897a6f56 Mon Sep 17 00:00:00 2001
From: Collin Winter <collinw@gmail.com>
Date: Fri, 20 Feb 2009 19:30:41 +0000
Subject: [PATCH] Issue 5176: special-case string formatting in BINARY_MODULO
 implementation. This shows a modest (1-3%) speed-up in templating systems,
 for example.

---
 Lib/test/test_opcodes.py | 6 ++++++
 Python/ceval.c           | 5 ++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_opcodes.py b/Lib/test/test_opcodes.py
index d7d1673a879..7985bf61a4d 100644
--- a/Lib/test/test_opcodes.py
+++ b/Lib/test/test_opcodes.py
@@ -102,6 +102,12 @@ class OpcodeTest(unittest.TestCase):
         g = eval('lambda a=1: None')
         self.assertNotEquals(f, g)
 
+    def test_modulo_of_string_subclasses(self):
+        class MyString(str):
+            def __mod__(self, value):
+                return 42
+        self.assertEqual(MyString() % 3, 42)
+
 
 def test_main():
     run_unittest(OpcodeTest)
diff --git a/Python/ceval.c b/Python/ceval.c
index d457fd54894..419ecfaaaaa 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1283,7 +1283,10 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 		case BINARY_MODULO:
 			w = POP();
 			v = TOP();
-			x = PyNumber_Remainder(v, w);
+			if (PyString_CheckExact(v))
+				x = PyString_Format(v, w);
+			else
+				x = PyNumber_Remainder(v, w);
 			Py_DECREF(v);
 			Py_DECREF(w);
 			SET_TOP(x);