SF bug #541883 (Vincent Fiack).

A stupid bug in object_set_class(): didn't check for value==NULL
before checking its type.

Bugfix candidate.

Lib/test/test_descr.py

@@ -2352,6 +2352,12 @@ def setclass():
             pass
         else:
             raise TestFailed, "shouldn't allow %r.__class__ = %r" % (x, C)
+        try:
+            delattr(x, "__class__")
+        except TypeError:
+            pass
+        else:
+            raise TestFailed, "shouldn't allow del %r.__class__" % x
     cant(C(), list)
     cant(list(), C)
     cant(C(), 1)

Objects/typeobject.c

@@ -1605,6 +1605,11 @@ object_set_class(PyObject *self, PyObject *value, void *closure)
 	PyTypeObject *old = self->ob_type;
 	PyTypeObject *new, *newbase, *oldbase;
 
+	if (value == NULL) {
+		PyErr_SetString(PyExc_TypeError,
+				"can't delete __class__ attribute");
+		return -1;
+	}
 	if (!PyType_Check(value)) {
 		PyErr_Format(PyExc_TypeError,
 		  "__class__ must be set to new-style class, not '%s' object",