Pass a tuple (or list) to a C wrapper function

[Java and Swing]

I have a C function which takes an array of long values..

I understand that I can pass a tuple to a C wrapper function and in the
C wrapper function have..

int ok = PyArg_ParseTupl e(args, "s(ll)", &a, &b, &c);

...that's great if my tuple only contained two longs..but what if it
contained 50
would I have to do..

int ok = PyArg_ParseTupl e(args, "s(llllllllllll llllll....ll)", &a, &b,
&c, &d...) ??

how can I handle this?

[Jeremy Moles]

Re: Pass a tuple (or list) to a C wrapper function

It depends on how you want to manipulate the data in C. If you want
compile-time variable access to each float, yeah, 50 floats. :)

Probably what you want to do though is just keep the tuple as is and
iterate over it using the PySequence_* protocol:

http://docs.python.org/api/sequence.html

On Wed, 2005-10-12 at 13:06 -0700, Java and Swing wrote:[color=blue]
> I have a C function which takes an array of long values..
>
> I understand that I can pass a tuple to a C wrapper function and in the
> C wrapper function have..
>
> int ok = PyArg_ParseTupl e(args, "s(ll)", &a, &b, &c);
>
> ..that's great if my tuple only contained two longs..but what if it
> contained 50
> would I have to do..
>
> int ok = PyArg_ParseTupl e(args, "s(llllllllllll llllll....ll)", &a, &b,
> &c, &d...) ??
>
> how can I handle this?
>[/color]

[Fredrik Lundh]

Re: Pass a tuple (or list) to a C wrapper function

Jeremy Moles wrote:
[color=blue]
> Probably what you want to do though is just keep the tuple as is and
> iterate over it using the PySequence_* protocol:
>
> http://docs.python.org/api/sequence.html[/color]

I did post a complete and tested example a few days ago, which contained
code that showed how to do this. a complete waste of time, of course.

</F>

[Java and Swing]

Re: Pass a tuple (or list) to a C wrapper function

Fredrik...I forgot about that...wish Google Groups had a way to quickly
find the topics a user posts.

anyhow, for receiving an object from python..is it

ok = PyArg_ParseTupl e(args, "sO", &x, &y);

....is it "sO" or "s0" ....is it O (as in the letter) or 0 (as in the
number)? I would think "O" the letter..but it looks like a zero.

thanks

Fredrik Lundh wrote:[color=blue]
> Jeremy Moles wrote:
>[color=green]
> > Probably what you want to do though is just keep the tuple as is and
> > iterate over it using the PySequence_* protocol:
> >
> > http://docs.python.org/api/sequence.html[/color]
>
> I did post a complete and tested example a few days ago, which contained
> code that showed how to do this. a complete waste of time, of course.
>
> </F>[/color]

[Java and Swing]

Re: Pass a tuple (or list) to a C wrapper function

Fredrik,
...I tried using your code...

static long *get_long_array (PyObject *data, int *data_size) {
int i, size;
long* out;
PyObject* seq;

seq = PySequence_Fast (data, "expected a sequence");
if (!seq)
return NULL;

size = PySequence_Size (seq);
if (size < 0)
return NULL;

if (data_size)
*data_size = size;

out = (long*) PyMem_Malloc(si ze * sizeof(long));
if (!out) {
Py_DECREF(seq);
PyErr_NoMemory( );
return NULL;
}

for (i = 0; i < size; i++)
out[i] = PyInt_AsLong(Py Sequence_Fast_G ET_ITEM(seq, i));

Py_DECREF(seq);

if (PyErr_Occurred ()) {
PyMem_Free(out) ;
out = NULL;
}

return out;

}


and I get this error..

C:\project\myap p.c(549) : error C2040: 'get_long_array ' : 'long
*(struct _object *,int *)' differs in levels of indirection from 'int
()'

any idea?

Fredrik Lundh wrote:[color=blue]
> Jeremy Moles wrote:
>[color=green]
> > Probably what you want to do though is just keep the tuple as is and
> > iterate over it using the PySequence_* protocol:
> >
> > http://docs.python.org/api/sequence.html[/color]
>
> I did post a complete and tested example a few days ago, which contained
> code that showed how to do this. a complete waste of time, of course.
>
> </F>[/color]

[Java and Swing]

Re: Pass a tuple (or list) to a C wrapper function

I got it. I had get_long_array placed after the method that was
calling it..
i.e.

void doStuf(...) {
x = get_long_array( ...);
}

static long *get_long_array (PyObject *data, int *data_size) {
....
}

....I put get_long_array before it in my code..and its fine.

Thanks

Java and Swing wrote:[color=blue]
> Fredrik,
> ...I tried using your code...
>
> static long *get_long_array (PyObject *data, int *data_size) {
> int i, size;
> long* out;
> PyObject* seq;
>
> seq = PySequence_Fast (data, "expected a sequence");
> if (!seq)
> return NULL;
>
> size = PySequence_Size (seq);
> if (size < 0)
> return NULL;
>
> if (data_size)
> *data_size = size;
>
> out = (long*) PyMem_Malloc(si ze * sizeof(long));
> if (!out) {
> Py_DECREF(seq);
> PyErr_NoMemory( );
> return NULL;
> }
>
> for (i = 0; i < size; i++)
> out[i] = PyInt_AsLong(Py Sequence_Fast_G ET_ITEM(seq, i));
>
> Py_DECREF(seq);
>
> if (PyErr_Occurred ()) {
> PyMem_Free(out) ;
> out = NULL;
> }
>
> return out;
>
> }
>
>
> and I get this error..
>
> C:\project\myap p.c(549) : error C2040: 'get_long_array ' : 'long
> *(struct _object *,int *)' differs in levels of indirection from 'int
> ()'
>
> any idea?
>
> Fredrik Lundh wrote:[color=green]
> > Jeremy Moles wrote:
> >[color=darkred]
> > > Probably what you want to do though is just keep the tuple as is and
> > > iterate over it using the PySequence_* protocol:
> > >
> > > http://docs.python.org/api/sequence.html[/color]
> >
> > I did post a complete and tested example a few days ago, which contained
> > code that showed how to do this. a complete waste of time, of course.
> >
> > </F>[/color][/color]

[Fredrik Lundh]

Re: Pass a tuple (or list) to a C wrapper function

Java and Swing wrote:
[color=blue]
> and I get this error..
>
> C:\project\myap p.c(549) : error C2040: 'get_long_array ' : 'long
> *(struct _object *,int *)' differs in levels of indirection from 'int
> ()'[/color]

so what's on line 549 in myapp.c?

what other warnings did you get from the compiler?

do you have other things named "get_long_array " in your program ?

(I'm really beginning to think that you should take a break and learn
a little more C before continuing on this task; C isn't that hard, but
it's not really a language you can use to write programs by trial and
error...)

</F>

[Fredrik Lundh]

Re: Pass a tuple (or list) to a C wrapper function

"Java and Swing" wrote:
[color=blue]
> anyhow, for receiving an object from python..is it
>
> ok = PyArg_ParseTupl e(args, "sO", &x, &y);
>
> ...is it "sO" or "s0" ....is it O (as in the letter) or 0 (as in the
> number)? I would think "O" the letter..but it looks like a zero.[/color]

eh? if you're not sure, what keeps you from cutting and pasting ?
or comparing it visually with characters that you type in yourself ?

(it's the letter O, for Object. the corresponding variable must be a
pointer to a PyObject pointer. see the documentation for details:

http://www.python.org/doc/current/api/arg-parsing.html

)

</F>