Add a format specifier %R to PyUnicode_FromFormat(), which embeds the result of a call to PyObject_Repr() into the string. This makes it possible to simplify many repr implementations. PyUnicode_FromFormat() uses two steps to create the final string: A first pass through the format string determines the size of the final string and a second pass creates the string. To avoid calling PyObject_Repr() twice for each %R specifier, PyObject_Repr() is called during the size calculation step and the results are stored in an array (whose size is determined at the start by counting %R specifiers).

--- a/Modules/_tkinter.c	Fri May 18 22:12:08 2007 +0000
+++ b/Modules/_tkinter.c	Sat May 19 21:49:49 2007 +0000
@@ -809,10 +809,8 @@
 static PyObject *
 PyTclObject_repr(PyTclObject *self)
 {
-	char buf[50];
-	PyOS_snprintf(buf, 50, "<%s object at %p>",
-		      self->value->typePtr->name, self->value);
-	return PyUnicode_FromString(buf);
+	return PyUnicode_FromFormat("<%s object at %p>",
+	                            self->value->typePtr->name, self->value);
 }
 
 static int