Optimize reversed(list) using a custom iterator.

diff --git a/Objects/enumobject.c b/Objects/enumobject.c
index 998e3810a1dd17a3f196b052d126b9c89837f110..8b2e6e116ba10861b49af06f19f78e8559351aaf 100644 (file)
--- a/Objects/enumobject.c
+++ b/Objects/enumobject.c
@@ -174,8 +174,8 @@ reversed_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
        if (!PyArg_UnpackTuple(args, "reversed", 1, 1, &seq))
                return NULL;
 
-       /* Special case optimization for xrange */
-       if (PyRange_Check(seq))
+       /* Special case optimization for xrange and lists */
+       if (PyRange_Check(seq) || PyList_Check(seq))
                return PyObject_CallMethod(seq, "__reversed__", NULL);
 
        if (!PySequence_Check(seq)) {

diff --git a/Objects/listobject.c b/Objects/listobject.c
index fd98b639a9a8e7f61e4018e2936cb02fe0d54d8c..cf00ab24a8b7acb5df887d9979763e2934412eb7 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -2349,6 +2349,11 @@ list_nohash(PyObject *self)
        return -1;
 }
 
+static PyObject *list_iter(PyObject *seq);
+static PyObject *list_reversed(PyListObject* seq, PyObject* unused);
+
+PyDoc_STRVAR(reversed_doc,
+"L.__reversed__() -- return a reverse iterator over the list");
 PyDoc_STRVAR(append_doc,
 "L.append(object) -- append object to end");
 PyDoc_STRVAR(extend_doc,
@@ -2373,6 +2378,7 @@ PyDoc_STRVAR(sorted_doc,
 cmp(x, y) -> -1, 0, 1");
 
 static PyMethodDef list_methods[] = {
+       {"__reversed__",(PyCFunction)list_reversed, METH_NOARGS, reversed_doc},
        {"append",      (PyCFunction)listappend,  METH_O, append_doc},
        {"insert",      (PyCFunction)listinsert,  METH_VARARGS, insert_doc},
        {"extend",      (PyCFunction)listextend,  METH_O, extend_doc},
@@ -2404,8 +2410,6 @@ PyDoc_STRVAR(list_doc,
 "list() -> new list\n"
 "list(sequence) -> new list initialized from sequence's items");
 
-static PyObject *list_iter(PyObject *seq);
-
 static PyObject *
 list_subscript(PyListObject* self, PyObject* item)
 {
@@ -2760,3 +2764,93 @@ PyTypeObject PyListIter_Type = {
        0,                                      /* tp_descr_get */
        0,                                      /* tp_descr_set */
 };
+
+/*********************** List Reverse Iterator **************************/
+
+typedef struct {
+       PyObject_HEAD
+       long it_index;
+       PyListObject *it_seq;
+} listreviterobject;
+
+PyTypeObject PyListRevIter_Type;
+
+static PyObject *
+list_reversed(PyListObject *seq, PyObject *unused)
+{
+       listreviterobject *it;
+
+       it = PyObject_GC_New(listreviterobject, &PyListRevIter_Type);
+       if (it == NULL)
+               return NULL;
+       assert(PyList_Check(seq));
+       it->it_index = PyList_GET_SIZE(seq) - 1;
+       Py_INCREF(seq);
+       it->it_seq = seq;
+       PyObject_GC_Track(it);
+       return (PyObject *)it;
+}
+
+static void
+listreviter_dealloc(listreviterobject *it)
+{
+       PyObject_GC_UnTrack(it);
+       Py_XDECREF(it->it_seq);
+       PyObject_GC_Del(it);
+}
+
+static int
+listreviter_traverse(listreviterobject *it, visitproc visit, void *arg)
+{
+       if (it->it_seq == NULL)
+               return 0;
+       return visit((PyObject *)it->it_seq, arg);
+}
+
+static PyObject *
+listreviter_next(listreviterobject *it)
+{
+       PyObject *item = NULL;
+
+       assert(PyList_Check(it->it_seq));
+       if (it->it_index >= 0) {
+               assert(it->it_index < PyList_GET_SIZE(it->it_seq));
+               item = PyList_GET_ITEM(it->it_seq, it->it_index);
+               it->it_index--;
+               Py_INCREF(item);
+       }
+       return item;
+}
+
+PyTypeObject PyListRevIter_Type = {
+       PyObject_HEAD_INIT(&PyType_Type)
+       0,                                      /* ob_size */
+       "listreverseiterator",                  /* tp_name */
+       sizeof(listreviterobject),              /* tp_basicsize */
+       0,                                      /* tp_itemsize */
+       /* methods */
+       (destructor)listreviter_dealloc,        /* tp_dealloc */
+       0,                                      /* tp_print */
+       0,                                      /* tp_getattr */
+       0,                                      /* tp_setattr */
+       0,                                      /* tp_compare */
+       0,                                      /* tp_repr */
+       0,                                      /* tp_as_number */
+       0,                                      /* tp_as_sequence */
+       0,                                      /* tp_as_mapping */
+       0,                                      /* tp_hash */
+       0,                                      /* tp_call */
+       0,                                      /* tp_str */
+       PyObject_GenericGetAttr,                /* tp_getattro */
+       0,                                      /* tp_setattro */
+       0,                                      /* tp_as_buffer */
+       Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
+       0,                                      /* tp_doc */
+       (traverseproc)listreviter_traverse,     /* tp_traverse */
+       0,                                      /* tp_clear */
+       0,                                      /* tp_richcompare */
+       0,                                      /* tp_weaklistoffset */
+       PyObject_SelfIter,                      /* tp_iter */
+       (iternextfunc)listreviter_next,         /* tp_iternext */
+       0,
+};