Issue #8268: Old-style classes (not just instances) now support weak

references.

Include/classobject.h

@@ -18,6 +18,7 @@ typedef struct {
     PyObject	*cl_getattr;
     PyObject	*cl_setattr;
     PyObject	*cl_delattr;
+    PyObject    *cl_weakreflist; /* List of weak references */
 } PyClassObject;
 
 typedef struct {

Lib/test/test_sys.py

@@ -544,7 +544,7 @@ class SizeofTest(unittest.TestCase):
         class class_oldstyle():
             def method():
                 pass
-        check(class_oldstyle, size(h + '6P'))
+        check(class_oldstyle, size(h + '7P'))
         # instance (old-style class)
         check(class_oldstyle(), size(h + '3P'))
         # instancemethod (old-style class)

Lib/test/test_weakref.py

@@ -685,6 +685,26 @@ class ReferencesTestCase(TestBase):
         # No exception should be raised here
         gc.collect()
 
+    def test_classes(self):
+        # Check that both old-style classes and new-style classes
+        # are weakrefable.
+        class A(object):
+            pass
+        class B:
+            pass
+        l = []
+        weakref.ref(int)
+        a = weakref.ref(A, l.append)
+        A = None
+        gc.collect()
+        self.assertEqual(a(), None)
+        self.assertEqual(l, [a])
+        b = weakref.ref(B, l.append)
+        B = None
+        gc.collect()
+        self.assertEqual(b(), None)
+        self.assertEqual(l, [a, b])
+
 
 class SubclassableWeakrefTestCase(TestBase):
 

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.7 beta 1?
 Core and Builtins
 -----------------
 
+- Issue #8268: Old-style classes (not just instances) now support weak
+  references.
+
 - Issue #8211: Save/restore CFLAGS around AC_PROG_CC in configure.in, compiler
   optimizations are disabled when --with-pydebug is used.
 

Objects/classobject.c

@@ -123,6 +123,7 @@ alloc_error:
 	op->cl_dict = dict;
 	Py_XINCREF(name);
 	op->cl_name = name;
+	op->cl_weakreflist = NULL;
 
 	op->cl_getattr = class_lookup(op, getattrstr, &dummy);
 	op->cl_setattr = class_lookup(op, setattrstr, &dummy);
@@ -188,6 +189,8 @@ static void
 class_dealloc(PyClassObject *op)
 {
 	_PyObject_GC_UNTRACK(op);
+	if (op->cl_weakreflist != NULL)
+		PyObject_ClearWeakRefs((PyObject *) op);
 	Py_DECREF(op->cl_bases);
 	Py_DECREF(op->cl_dict);
 	Py_XDECREF(op->cl_name);
@@ -454,7 +457,7 @@ PyTypeObject PyClass_Type = {
 	(traverseproc)class_traverse,		/* tp_traverse */
  	0,					/* tp_clear */
 	0,					/* tp_richcompare */
-	0,					/* tp_weaklistoffset */
+	offsetof(PyClassObject, cl_weakreflist), /* tp_weaklistoffset */
 	0,					/* tp_iter */
 	0,					/* tp_iternext */
 	0,					/* tp_methods */