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Optimize reversed(list) using a custom iterator.

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This commit is contained in:
Raymond Hettinger 2003-11-07 15:38:09 +00:00
parent ff1f194982
commit 1021c44b41
2 changed files with 98 additions and 4 deletions
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4
Objects/enumobject.c
View file

@ -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)) {

98
Objects/listobject.c
View file

@ -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,
};