Index: Lib/collections.py
===================================================================
--- Lib/collections.py	(revision 84821)
+++ Lib/collections.py	(working copy)
@@ -162,6 +162,15 @@
             link.next = first
             root.next = first.prev = link
 
+    def __sizeof__(self):
+        sizeof = _sys.getsizeof
+        n = len(self) + 1                       # number of links including root
+        size = sizeof(self.__dict__)            # instance dictionary
+        size += sizeof(self.__map) * 2          # internal dict and inherited dict
+        size += sizeof(self.__hardroot) * n     # link objects
+        size += sizeof(self.__root) * n         # proxy objects
+        return size
+
     setdefault = MutableMapping.setdefault
     update = MutableMapping.update
     pop = MutableMapping.pop