PyArg_ParseTupleAndKeywords in Python3.1

[Emeka]

Case,

Thanks so much! However, I am still confused. This is what I understood;

foo (a = "a", b = "b") so function , foo,  has default values which are "a"
and "b". pointer kwlist[] is a way of specifying default values .

Regards,
Emeka

On Fri, Dec 18, 2009 at 3:02 PM, Case Vanhorsen <casevh at gmail.com> wrote:

> On Fri, Dec 18, 2009 at 2:26 AM, Emeka <emekamicro at gmail.com> wrote:
> >    char *kwlist[] = {"a", "b", NULL};
> >    if (!PyArg_ParseTupleAndKeywords(args, kwrds, "|CC", kwlist, &a,
> > &b))
> > I am yet to understand what pointer kwlist[] does and why it is needed?
> > Regards,
> > Emeka
>
> foo is designed to accept two arguments that can be specified by
> either position or name. kwlist contains the legal keyword names. In
> this example, the legal keywords are 'a' and 'b'. That they match the
> names of the C variables is just a lucky coincidence. If you want to
> change the keyword names to 'foo' and 'bar', you would just use char
> *kwlist[]={"foo", "bar", NULL}.
>
> casevh
> >
> > On Fri, Dec 18, 2009 at 8:17 AM, casevh <casevh at gmail.com> wrote:
> >>
> >> On Dec 17, 11:14 am, Joachim Dahl <dahl.joac... at gmail.com> wrote:
> >> > In the Ubuntu 9.10 version of Python 3.1 (using your patch), there's a
> >> > related bug:
> >> >
> >> > >>> foo(b='b')
> >> >
> >> > will set the value of a in the extension module to zero, thus clearing
> >> > whatever
> >> > default value it may have had.  In other words, the optional character
> >> > arguments
> >> > that are skipped seem to be nulled by PyArg_ParseTupleAndKeywords().
> >>
> >> The following code seems to work fine for me:
> >>
> >> static PyObject* foo(PyObject *self, PyObject *args, PyObject *kwrds)
> >> {
> >>    int a=65, b=66;
> >>    char *kwlist[] = {"a", "b", NULL};
> >>    if (!PyArg_ParseTupleAndKeywords(args, kwrds, "|CC", kwlist, &a,
> >> &b))
> >>        return NULL;
> >>    return Py_BuildValue("(CC)", a, b);
> >> }
> >>
> >> The default values seem to remain as 'A' and 'B'.
> >>
> >> >>> foo()
> >> ('A', 'B')
> >> >>> foo(b='b')
> >> ('A', 'b')
> >> >>> foo()
> >> ('A', 'B')
> >> >>> foo('a')
> >> ('a', 'B')
> >> >>> foo('a', b='b')
> >> ('a', 'b')
> >> >>> foo()
> >> ('A', 'B')
> >> >>>
> >>
> >> casevh
> >> --
> >> http://mail.python.org/mailman/listinfo/python-list
> >
> >
>
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