PEP 205, Weak References -- initial checkin.
diff --git a/Include/classobject.h b/Include/classobject.h
index 8fde040..06c178f 100644
--- a/Include/classobject.h
+++ b/Include/classobject.h
@@ -24,6 +24,7 @@
     PyObject_HEAD
     PyClassObject *in_class;	/* The class object */
     PyObject	  *in_dict;	/* A dictionary */
+    PyObject	  *in_weakreflist; /* List of weak references */
 } PyInstanceObject;
 
 typedef struct {