Re: embedding and extending python C API registering callback handlerobjects

[Tim Spens]

--- On Fri, 6/27/08, Tim Spens <t_*****@yahoo.comwrote:

From: Tim Spens <t_*****@yahoo.com>
Subject: Re: embedding and extending python C API registering callback handler objects
To: py*********@python.org, "Matimus" <mc******@gmail.com>
Date: Friday, June 27, 2008, 9:16 AM
thanks, but didn't fix the problem.
--- On Fri, 6/27/08, Matimus <mc******@gmail.com>
wrote:

From: Matimus <mc******@gmail.com>
Subject: Re: embedding and extending python C API

registering callback handler objects

To: py*********@python.org
Date: Friday, June 27, 2008, 9:03 AM
On Jun 27, 8:22 am, Tim Spens

<[e-mail]>

wrote:

Hello all,
>
I've been trying to get an example found

herehttp://codeidol.com/python/python3/Embedding-Python/Registering-Callb...

to work. Every thing works fine except when I

try to

trigger an event from c that will call a python

function.

Here is my test code:

>
//-----------------------python

code--------------------------//

#! /usr/bin/env python
import time
import callback
>
def callback1(label,count):
print 'callback1 successfully

triggered from python via callback.so'

return 'callback1 =%s number

%i' % (label, count)

>
def callback2(label,count):
return 'callback2 =' +

label * count

>
print '\nTest1:'
callback.setHandler(callback1)
callback.triggerEvent() # simulate events

caught by C layer

>
print '\nTest2:'
callback.setHandler(callback2)
>
print 'Waiting for callback2 to be called

from

c:'

while 1:
time.sleep(.001)
>
//-----------------------c

code-------------------------------//

#include <Python.h>
#include <stdlib.h>
>
/* keep Python object in C */
static PyObject *Handler = NULL;
>
void Route_Event(char *label, int count){
char *cres;
PyObject *args, *pres;
/* call Python handler */
args = Py_BuildValue("(si)", label,

count);

pres = PyEval_CallObject(Handler, args);
Py_DECREF(args);
if (pres != NULL){
/* use and decref handler result */
PyArg_Parse(pres, "s",

&cres);

printf("%s\n", cres);
Py_DECREF(pres);
>
}}
>
// the actual python callback call
static PyObject *
make_call(PyObject *function, PyObject *args){
if (function == NULL) return NULL;
PyObject * val =

PyObject_CallObject(function,

args);

Py_XDECREF(args);
return val;
>
}
>
static PyObject *
Register_Handler(PyObject *self, PyObject *args){
/* save Python callable object */
Py_XDECREF(Handler);
PyArg_Parse(args, "O",

&Handler);

Py_XINCREF(Handler);
Py_INCREF(Py_None);
return Py_None;
>
}
>
static PyObject *
Trigger_Event(PyObject *self, PyObject *args){
/* let Python simulate event caught by C */
static int count = 0;
Route_Event("spam", count++);
Py_INCREF(Py_None);
return Py_None;
>
}
>
static struct PyMethodDef callback_methods[] = {
{"setHandler",

Register_Handler},

/* name, address */

{"triggerEvent", Trigger_Event},
{NULL, NULL}};
>
>

/* on first "import callback" */

void initcallback(){ /* this

is called by Python */

(void) Py_InitModule("callback",

callback_methods);

>
}
>
int main(){
while (1){
printf("1\n");
//attempting to call callback2

which is registered to Handler

//i've also tried args =

Py_BuildValue("(si)", label, count); here

but I

get a segfault.

PyObject *args =

Py_BuildValue("s","c code");

printf("2\n");
PyObject* val =

make_call(Handler,args);

printf("3\n");
Py_XDECREF (val);
printf("4\n");
sleep(1);
>
}}
>
//------------------------compiler

stuff----------------------//

gcc callback.c -c -g -Wall -fpic -I

/usr/include/python2.5 -o callback.o

gcc callback.c -g -Wall -I /usr/include/python2.5

-L

/usr/local/lib -lpython2.5 -o callback

gcc -shared -Wall callback.o -o callback.so
>
//------------------------test code

results-------------------//

../callback.py
Test1:
callback1 successfully triggered from python via

callback.so

callback1 =spam number 0
>
Test2:
Waiting for callback2 to be called from c:
#NOTHING EVER GETS PRINTED HERE CALLBACK NEVER

GETS

CALLED?

>
../callback
1
2
3
4
....
>
Thanks,
Tim

Maybe you just need to flush the stdout buffer in

python.

`sys.stdout.flush()`

Matt
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I think I know where the problem is but I'm unsure how to fix it. When I call Register_Handler(...) from python via callback.setHandler1(callback1) this only seems to affect pythons ability to trigger an "event" in c. PyObject *Handler is always NULL even after I call Register_Handler(...). I thought there was some magic here that was assigning the pointer *Handler to my python callback1 handler so it could be triggered from c?

-Tim