On 01/15/2014 09:37 PM, Guido van Rossum wrote:
Well, I think these are mostly artifacts from old times, and usually
passing None *should* be the same as omitting the argument. But check
each case!
Vajrasky Kok's recent posting to python-dev discusses the same problem.
His example is itertools.repeat's second parameter, which is slightly
nastier. Consider the implementation:
static PyObject *
repeat_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
repeatobject *ro;
PyObject *element;
Py_ssize_t cnt = -1;
static char *kwargs[] = {"object", "times", NULL};
if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|n:repeat", kwargs,
&element, &cnt))
return NULL;
if (PyTuple_Size(args) == 2 && cnt < 0)
cnt = 0;
I draw your attention to the last two lines. And remember, Argument
Clinic doesn't provide the "args" and "kwargs" parameters to the "impl"
function. That means two things:
* itertools.repeat deliberately makes it impossible to provide an
argument for "times" that behaves the same as not providing the
"times" argument, and
* there is currently no way to implement this behavior using Argument
Clinic. (I'd have to add a hack where impl functions also get args
and kwargs.)
Passing in "None" here is inconvenient as it's an integer argument. -1
actually seems like a pretty sane default to mean "repeat forever", but
the author has gone to some effort to prevent this. I therefore assume
they had a very good reason. So again we seem stuck.
Are you suggesting that, when converting builtins to Argument Clinic
with unrepresentable default values, we're permitted to tweak the
defaults to something representable?
//arry/
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
