From a57df2cf1d627840dff505e8487fbd5f42414c7b Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Wed, 31 Mar 2010 21:32:15 +0000
Subject: Issue #8268: Old-style classes (not just instances) now support weak
 references.

---
 Include/classobject.h    |  1 +
 Lib/test/test_sys.py     |  2 +-
 Lib/test/test_weakref.py | 20 ++++++++++++++++++++
 Misc/NEWS                |  3 +++
 Objects/classobject.c    |  5 ++++-
 5 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/Include/classobject.h b/Include/classobject.h
index 118dd09..bc03e0d 100644
--- a/Include/classobject.h
+++ b/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 {
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index d106fe7..1720875 100644
--- a/Lib/test/test_sys.py
+++ b/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)
diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index 536a987..bc2982f 100644
--- a/Lib/test/test_weakref.py
+++ b/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):
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 09d07f2..80f1d2e 100644
--- a/Misc/NEWS
+++ b/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.
 
diff --git a/Objects/classobject.c b/Objects/classobject.c
index 3f51c0f..032d354 100644
--- a/Objects/classobject.c
+++ b/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 */
-- 
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