Use Py_VISIT in all tp_traverse methods, instead of traversing manually or using a custom, nearly-identical macro. This probably changes how some of these functions are compiled, which may result in fractionally slower (or faster) execution. Considering the nature of traversal, visiting much of the address space in unpredictable patterns, I'd argue the code readability and maintainability is well worth it ;P

--- a/Objects/cellobject.c	Sat Apr 15 21:41:56 2006 +0000
+++ b/Objects/cellobject.c	Sat Apr 15 21:47:09 2006 +0000
@@ -73,8 +73,7 @@
 static int
 cell_traverse(PyCellObject *op, visitproc visit, void *arg)
 {
-	if (op->ob_ref)
-		return visit(op->ob_ref, arg);
+	Py_VISIT(op->ob_ref);
 	return 0;
 }