Raymond Hettinger wrote:
> FWIW, the deque() approach becomes even faster in Py2.7 and Py3.1
> which has a high-speed path for the case where maxlen is zero.
> Here's a snippet from Modules/_collectionsmodule.c:
>
> /* Run an iterator to exhaustion. Shortcut for
> the extend/extendleft methods when maxlen == 0. */
> static PyObject*
> consume_iterator(PyObject *it)
> {
> PyObject *item;
>
> while ((item = PyIter_Next(it)) != NULL) {
> Py_DECREF(item);
> }
> Py_DECREF(it);
> if (PyErr_Occurred())
> return NULL;
> Py_RETURN_NONE;
> }
>
>
> This code consumes an iterator to exhaustion.
> It is short, sweet, and hard to beat.
islice() is still a tad faster. A possible optimization:
static PyObject*
consume_iterator(PyObject *it)
{
PyObject *item;
PyObject *(*iternext)(PyObject *);
iternext = *Py_TYPE(it)->tp_iternext;
while ((item = iternext(it)) != NULL) {
Py_DECREF(item);
}
Py_DECREF(it);
if (PyErr_Occurred()) {
if(PyErr_ExceptionMatches(PyExc_StopIteration))
PyErr_Clear();
else
return NULL;
}
Py_RETURN_NONE;
}
Before:
$ ./python -m timeit -s"from itertools import repeat, islice; from
collections import deque; from sys import maxint" "next(islice(repeat(None,
1000), maxint, maxint), None)"
100000 loops, best of 3: 6.49 usec per loop
$ ./python -m timeit -s"from itertools import repeat, islice; from
collections import deque; from sys import maxint" "deque(repeat(None, 1000),
maxlen=0)"
100000 loops, best of 3: 9.93 usec per loop
After:
$ ./python -m timeit -s"from itertools import repeat, islice; from
collections import deque; from sys import maxint" "deque(repeat(None, 1000),
maxlen=0)"
100000 loops, best of 3: 6.31 usec per loop
Peter
PS: Two more, for Paul Rubin:
$ ./python -m timeit -s"from itertools import repeat" "sum(0 for _ in
repeat(None, 1000))"
10000 loops, best of 3: 125 usec per loop
$ ./python -m timeit -s"from itertools import repeat" "sum(0 for _ in
repeat(None, 1000) if 0)"
10000 loops, best of 3: 68.3 usec per loop
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