Let reversed() work with itself.

Include/listobject.h

@@ -22,6 +22,7 @@ extern "C" {
 typedef struct {
     PyObject_VAR_HEAD
     PyObject **ob_item;
+    int allocated;
 } PyListObject;
 
 PyAPI_DATA(PyTypeObject) PyList_Type;

Lib/test/test_enumerate.py

@@ -141,6 +141,10 @@ class TestReversed(unittest.TestCase):
         x = xrange(1)
         self.assertEqual(type(reversed(x)), type(iter(x)))
 
+    def test_double_reverse(self):
+        s = 'hello'
+        self.assertEqual(list(reversed(reversed(s))), list(s))
+
 def test_main(verbose=None):
     testclasses = (EnumerateTestCase, SubclassTestCase, TestEmpty, TestBig,
                    TestReversed)

Objects/enumobject.c

@@ -230,11 +230,22 @@ reversed_next(reversedobject *ro)
 	return item;
 }
 
+static PyObject *
+reversed_reverse(reversedobject *ro, PyObject *unused)
+{
+	return PyObject_GetIter(ro->seq);
+}
+
 PyDoc_STRVAR(reversed_doc,
 "reverse(sequence) -> reverse iterator over values of the sequence\n"
 "\n"
 "Return a reverse iterator");
 
+static PyMethodDef reversed_methods[] = {
+	{"__reversed__",	(PyCFunction)reversed_reverse,	
+		METH_NOARGS,	 reversed_doc},
+};
+
 PyTypeObject PyReversed_Type = {
 	PyObject_HEAD_INIT(&PyType_Type)
 	0,                              /* ob_size */
@@ -266,7 +277,7 @@ PyTypeObject PyReversed_Type = {
 	0,                              /* tp_weaklistoffset */
 	PyObject_SelfIter,		/* tp_iter */
 	(iternextfunc)reversed_next,    /* tp_iternext */
-	0,                              /* tp_methods */
+	reversed_methods,               /* tp_methods */
 	0,                              /* tp_members */
 	0,                              /* tp_getset */
 	0,                              /* tp_base */