Issue 5176: special-case string formatting in BINARY_MODULO implementation. This shows a modest (1-3%) speed-up in templating systems, for example.
diff --git a/Python/ceval.c b/Python/ceval.c
index d457fd5..419ecfa 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1283,7 +1283,10 @@
 		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);