PyArg_ParseTupleAndKeywords in Python3.1

[Case Vanhorsen]

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
>
>