embedding and extending python C API registering callback handler objects

[Tim Spens]

thanks, but didn't fix the problem.


--- On Fri, 6/27/08, Matimus <mccredie at gmail.com> wrote:

> From: Matimus <mccredie at gmail.com>
> Subject: Re: embedding and extending python C API registering callback handler objects
> To: python-list at python.org
> Date: Friday, June 27, 2008, 9:03 AM
> On Jun 27, 8:22 am, Tim Spens <t_sp... at yahoo.com>
> 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
> --
> http://mail.python.org/mailman/listinfo/python-list