PyArg_ParseTupleAndKeywords in Python3.1

[Joachim Dahl]

I think that "C" encoding is what I need, however I run into an odd
problem.
If I use the following C code

static PyObject* foo(PyObject *self, PyObject *args, PyObject *kwrds)
{
  char a, b;
  char *kwlist[] = {"a", "b", NULL};
  if (!PyArg_ParseTupleAndKeywords(args, kwrds, "|CC", kwlist, &a,
&b))
    return NULL;
  ...

then the following works:
>>> foo('a')
>>> foo('a','b')
>>> foo(a='a',b='b')

but the following fails:
>>> foo(b='b')
RuntimeError: impossible<bad format char>: 'CC'

Is this error-message expected?

On Nov 30, 10:19 pm, casevh <cas... at gmail.com> wrote:
> On Nov 30, 1:04 pm, Joachim Dahl <dahl.joac... at gmail.com> wrote:
>
>
>
>
>
> > Obviously the name of the C function and the char variable cannot both
> > be foo,
> > so the C code should be:
>
> > static PyObject* foo(PyObject *self, PyObject *args, PyObject *kwrds)
> > {
> >   char foochar;
> >   char *kwlist[] = {"foochar", NULL};
> >   if (!PyArg_ParseTupleAndKeywords(args, kwrds, "c", kwlist,
> > &foochar))
> >     return NULL;
> >   ...
>
> > The question remains the same: why can't I pass a single character
> > argument to this function under Python3.1?
>
> > Thanks.
> > Joachim
>
> > On Nov 30, 9:52 pm, Joachim Dahl <dahl.joac... at gmail.com> wrote:
>
> > > I am updating an extension module from Python2.6 to Python3.
>
> > > I used to pass character codes to the extension module, for example, I
> > > would write:
>
> > > >>> foo('X')
>
> > > with the corresponding C extension routine defined as follows:
> > > static PyObject* foo(PyObject *self, PyObject *args, PyObject *kwrds)
> > > {
> > >   char foo;
> > >   char *kwlist[] = {"foo", NULL};
> > >   if (!PyArg_ParseTupleAndKeywords(args, kwrds, "c", kwlist, &foo))
> > >     return NULL;
> > >   ...
>
> > > In Python3.0 this also works, but in Python3.1 I get the following
> > > error:
> > > TypeError: argument 1 must be a byte string of length 1, not str
>
> > > and I seem to be supposed to write>>> foo(b'X')
>
> > > instead. From the Python C API, I have not been able to explain this
> > > new behavior.
> > > What is the correct way to pass a single character argument to
> > > Python3.1
> > > extension modules?- Hide quoted text -
>
> > - Show quoted text -
>
> Python 3.1 uses "c" (lowercase c) to parse a single character from a
> byte-string and uses "C" (uppercase c) to parse a single character
> from a Unicode string. I don't think there is an easy way to accept a
> character from both.
>
> HTH,
>
> casevh