return tuple from C to python (extending python)

[Kiran]

Hi all, I want to make python call some C functions, process them and
return them.

Ok, I got all the wrapper functions and everything setup right. Here
is my problem. What I need to do is to return a tuple from C to
python.

To go about doing this, I first create a tuple object in C doing the
following:

PyObject* toRet;
toRet = PyTuple_New(num _addr);

then, in a for loop, i assign values to the tuple as follows:

for ( i = 0; i < num_addr; i++ )
{
printf("%d\n", dat[i]);
PyTuple_SET_ITE M(toRet, i, (PyObject*)dat[i] );
}
(dat is declared as follows: unsigned int* dat; )

then, i say return toRet at the end of my C function.

when I try to print the tuple in python, it says the memory address
0x.... could not be written, and I can see a part of the tuple
printout, which is as follows:
( <nil>,
then i get my error.

can someone please help me with this?

thanks a lot!
-- Kiran

[Simon Forman]

Re: return tuple from C to python (extending python)

Kiran wrote:

Hi all, I want to make python call some C functions, process them and
return them.
>
Ok, I got all the wrapper functions and everything setup right. Here
is my problem. What I need to do is to return a tuple from C to
python.
>
To go about doing this, I first create a tuple object in C doing the
following:
>
PyObject* toRet;
toRet = PyTuple_New(num _addr);
>
then, in a for loop, i assign values to the tuple as follows:
>
for ( i = 0; i < num_addr; i++ )
{
printf("%d\n", dat[i]);
PyTuple_SET_ITE M(toRet, i, (PyObject*)dat[i] );
}
(dat is declared as follows: unsigned int* dat; )
>
then, i say return toRet at the end of my C function.
>
when I try to print the tuple in python, it says the memory address
0x.... could not be written, and I can see a part of the tuple
printout, which is as follows:
( <nil>,
then i get my error.
>
can someone please help me with this?
>
thanks a lot!
-- Kiran

I have not done a great deal of extension work with python, however, I
do not believe you can simply cast an int (or pointer to int, which is
what you say dat is declared as, unless my C is /really/ rusty) to
PyObject*.

I think you need to do something like Py_BuildValue(" i", 123), but see
http://docs.python.org/ext/buildValue.html for more info.

Peace,
~Simon

[Farshid Lashkari]

Re: return tuple from C to python (extending python)

Simon Forman wrote:

I have not done a great deal of extension work with python, however, I
do not believe you can simply cast an int (or pointer to int, which is
what you say dat is declared as, unless my C is /really/ rusty) to
PyObject*.
>
I think you need to do something like Py_BuildValue(" i", 123), but see
http://docs.python.org/ext/buildValue.html for more info.

Simon is correct. You need to create a python object from your unsigned
int. Try the following instead:

PyTuple_SET_ITE M(toRet, i, PyInt_FromLong( dat[i]) );

-Farshid

[Chetan]

Re: return tuple from C to python (extending python)

"Kiran" <Kiran.Karra@gm ail.comwrites:

PyObject* toRet;
toRet = PyTuple_New(num _addr);
>
then, in a for loop, i assign values to the tuple as follows:
>
for ( i = 0; i < num_addr; i++ )
{
printf("%d\n", dat[i]);
PyTuple_SET_ITE M(toRet, i, (PyObject*)dat[i] );
}
(dat is declared as follows: unsigned int* dat; )
>
then, i say return toRet at the end of my C function.
>
when I try to print the tuple in python, it says the memory address
0x.... could not be written, and I can see a part of the tuple
printout, which is as follows:
( <nil>,
then i get my error.
>

You could use PyInt_FromXXXX functions to convert dat[i] to PyInt

[Andrew Poelstra]

Re: return tuple from C to python (extending python)

On Tue, 2006-10-24 at 15:24 -0700, Kiran wrote:

Hi all, I want to make python call some C functions, process them and
return them.

Try comp.lang.pytho n
--
Andrew Poelstra <http://www.wpsoftware. net/projects/>

[Kiran]

Re: return tuple from C to python (extending python)


Farshid Lashkari wrote:

Simon Forman wrote:

I have not done a great deal of extension work with python, however, I
do not believe you can simply cast an int (or pointer to int, which is
what you say dat is declared as, unless my C is /really/ rusty) to
PyObject*.

I think you need to do something like Py_BuildValue(" i", 123), but see
http://docs.python.org/ext/buildValue.html for more info.

>
Simon is correct. You need to create a python object from your unsigned
int. Try the following instead:
>
PyTuple_SET_ITE M(toRet, i, PyInt_FromLong( dat[i]) );
>
-Farshid

That did the trick. thanks guys both for your help!