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Refactor list_extend() and list_fill() for gains in code size, memory 

utilization, and speed:

* Moved the responsibility for emptying the previous list from list_fill
  to list_init.

* Replaced the code in list_extend with the superior code from list_fill.

* Eliminated list_fill.

Results:

* list.extend() no longer creates an intermediate tuple except to handle
  the special case of x.extend(x).  The saves memory and time.

* list.extend(x) runs
    5 to 10% faster when x is a list or tuple
    15% faster when x is an iterable not defining __len__
    twice as fast when x is an iterable defining __len__

* the code is about 15 lines shorter and no longer duplicates
  functionality.
This commit is contained in:
Raymond Hettinger 2004-02-15 03:57:00 +00:00
parent ab517d2eac
commit 90a39bf12c
1 changed files with 71 additions and 84 deletions
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155
Objects/listobject.c
View File

@ -324,7 +324,6 @@ list_contains(PyListObject *a, PyObject *el)
return cmp;
}
static PyObject *
list_item(PyListObject *a, int i)
{
@ -686,7 +685,6 @@ listextend_internal(PyListObject *self, PyObject *b)
return 0;
}
static PyObject *
list_inplace_concat(PyListObject *self, PyObject *other)
{
@ -704,16 +702,70 @@ list_inplace_concat(PyListObject *self, PyObject *other)
static PyObject *
listextend(PyListObject *self, PyObject *b)
{
PyObject *it; /* iter(v) */
int m; /* size of self */
int n; /* guess for size of b */
int mn; /* m + n */
int i;
b = PySequence_Fast(b, "list.extend() argument must be iterable");
if (!b)
/* Special cases:
1) lists and tuples which can use PySequence_Fast ops
2) extending self to self requires making a copy first
*/
if (PyList_CheckExact(b) || PyTuple_CheckExact(b) || (PyObject *)self == b) {
b = PySequence_Fast(b, "argument must be iterable");
if (!b)
return NULL;
if (listextend_internal(self, b) < 0)
return NULL;
Py_RETURN_NONE;
}
it = PyObject_GetIter(b);
if (it == NULL)
return NULL;
if (listextend_internal(self, b) < 0)
return NULL;
/* Guess a result list size. */
n = PyObject_Size(b);
if (n < 0) {
PyErr_Clear();
n = 8; /* arbitrary */
}
m = self->ob_size;
mn = m + n;
if (list_resize(self, mn) == -1)
goto error;
memset(&(self->ob_item[m]), 0, sizeof(*self->ob_item) * n);
Py_INCREF(Py_None);
return Py_None;
/* Run iterator to exhaustion. */
for (i = m; ; i++) {
PyObject *item = PyIter_Next(it);
if (item == NULL) {
if (PyErr_Occurred())
goto error;
break;
}
if (i < mn)
PyList_SET_ITEM(self, i, item); /* steals ref */
else {
int status = ins1(self, self->ob_size, item);
Py_DECREF(item); /* append creates a new ref */
if (status < 0)
goto error;
}
}
/* Cut back result list if initial guess was too large. */
if (i < mn && self != NULL) {
if (list_ass_slice(self, i, mn, (PyObject *)NULL) != 0)
goto error;
}
Py_DECREF(it);
Py_RETURN_NONE;
error:
Py_DECREF(it);
return NULL;
}
static PyObject *
@ -2220,78 +2272,6 @@ list_richcompare(PyObject *v, PyObject *w, int op)
return PyObject_RichCompare(vl->ob_item[i], wl->ob_item[i], op);
}
/* Adapted from newer code by Tim */
static int
list_fill(PyListObject *result, PyObject *v)
{
PyObject *it; /* iter(v) */
int n; /* guess for result list size */
int i;
n = result->ob_size;
/* Special-case list(a_list), for speed. */
if (PyList_Check(v)) {
if (v == (PyObject *)result)
return 0; /* source is destination, we're done */
return list_ass_slice(result, 0, n, v);
}
/* Empty previous contents */
if (n != 0) {
if (list_ass_slice(result, 0, n, (PyObject *)NULL) != 0)
return -1;
}
/* Get iterator. There may be some low-level efficiency to be gained
* by caching the tp_iternext slot instead of using PyIter_Next()
* later, but premature optimization is the root etc.
*/
it = PyObject_GetIter(v);
if (it == NULL)
return -1;
/* Guess a result list size. */
n = PyObject_Size(v);
if (n < 0) {
PyErr_Clear();
n = 8; /* arbitrary */
}
if (list_resize(result, n) == -1)
goto error;
memset(result->ob_item, 0, sizeof(*result->ob_item) * n);
/* Run iterator to exhaustion. */
for (i = 0; ; i++) {
PyObject *item = PyIter_Next(it);
if (item == NULL) {
if (PyErr_Occurred())
goto error;
break;
}
if (i < n)
PyList_SET_ITEM(result, i, item); /* steals ref */
else {
int status = ins1(result, result->ob_size, item);
Py_DECREF(item); /* append creates a new ref */
if (status < 0)
goto error;
}
}
/* Cut back result list if initial guess was too large. */
if (i < n && result != NULL) {
if (list_ass_slice(result, i, n, (PyObject *)NULL) != 0)
goto error;
}
Py_DECREF(it);
return 0;
error:
Py_DECREF(it);
return -1;
}
static int
list_init(PyListObject *self, PyObject *args, PyObject *kw)
{
@ -2300,10 +2280,17 @@ list_init(PyListObject *self, PyObject *args, PyObject *kw)
if (!PyArg_ParseTupleAndKeywords(args, kw, "|O:list", kwlist, &arg))
return -1;
if (arg != NULL)
return list_fill(self, arg);
if (self->ob_size > 0)
return list_ass_slice(self, 0, self->ob_size, (PyObject*)NULL);
/* Empty previous contents */
if (self->ob_size != 0) {
if (list_ass_slice(self, 0, self->ob_size, (PyObject *)NULL) != 0)
return -1;
}
if (arg != NULL) {
PyObject *rv = listextend(self, arg);
if (rv == NULL)
return -1;
Py_DECREF(rv);
}
return 0;
}