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/_elementtree.c	Fri May 18 22:12:08 2007 +0000
+++ b/Modules/_elementtree.c	Sat May 19 21:49:49 2007 +0000
@@ -1118,17 +1118,7 @@
 static PyObject*
 element_repr(ElementObject* self)
 {
-    PyObject* repr;
-    char buffer[100];
-    
-    repr = PyUnicode_FromString("<Element ");
-
-    PyUnicode_AppendAndDel(&repr, PyObject_Repr(self->tag));
-
-    sprintf(buffer, " at %p>", self);
-    PyUnicode_AppendAndDel(&repr, PyUnicode_FromString(buffer));
-
-    return repr;
+    return PyUnicode_FromFormat("<Element %R at %p>", self->tag, self);
 }
 
 static PyObject*