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Thread: Error when trying to embed python into C++
Error when trying to embed python into C++
country flaguser name
United States		 2008-05-07 15:47:07 

  


  

    





Hi – I’m a newbie to doing this and would
appreciate any help / suggestions. Here’;s my problem, I have an existing
python application and a 3rd party C++ dll that need to talk to each
other. So far I have been able to follow the “Extending and Embedding

PythonR21; tutorial to create an extension to make the C++ dll available to
my python app and have it (the extension) return back values (ints, strings,
etc) to the python app.




 



The 3rd party dll has one method that I need to
use that requires a callback with a particular signature. My thinking is as
follows:



 



    
 
  1. create callback method in my
     python module
    2. 
 
  2. create a method in my C++
     extension that would take as a parameter the method from step 1 and store
     it
    3. 
 
  3. create another method in my C++
     extension that would act as the 3rd party dll callback with the
     particular signature
    4. 
 
  4. set the method in #3 to be the callback
     for the 3rd party dll
    5. 
 
  5. when the method in #3 is called
     back to from the 3rd party, parse the data into appropriate
     python objects and then call the python callback  from #2
    6. 




 



Problem is when I do this, I get a python.exe error and my
application crashes – so any ideas on what I am missing?? I don’t
have the option of using boost because this is a legacy application and do
cannot introduce another framework.



 



Again, any help is appreciated!



Thanks,



Erin



 



Here is the code:



 



Python



import wx




import camera_ext  #this is the C++ ext



 



class frmMain(wx.Frame):



    def _init_ctrls(self, prnt):



           ; #we
just initialize the controls on the form here




 



    def __init__(self, parent):



       

self._init_ctrls(parent)




    



   def OnInstallHooker(self, event):



        installed = camera_ext.InstallFrameHooker(self._my_frame_hooker) 
# is this right? Or should it be a module method, not a method of the class?



       

self.txtData.SetValue("installed hooker: " + str(installed));



        



    def OnStartGrab(self, event):



        started = camera_ext.StartFrameGrab()



       

self.txtData.SetValue("started grabbing: " + str(started));



        



 



    def _my_frame_hooker(self):



        # should be
called from the c++ ext



        print "I was
called"  # this never gets printed out ????




        return True




 



 



 






C++
(camera_ext)



 



 



static void FrameCallBack(
TProcessedDataProperty* Attributes, unsigned char *Frameptr )



{




 



         ;   //once
called, we need to package up to return it to python as an actual object



         ;   



         ;   PyObject
*arglist;



         ;   PyObject
*result;



 



         ;   printf(220;fooR21;)
//this does print out so I know the 3rdparty dll (BUFUSB is calling back)



 



         ;   //
All frame data is pointed by Frameptr



         ;   //
All frame related attributes is in Attributes.



         ;   arglist
= Py_BuildValue("i", Attributes->CameraID);



         ;   result
= PyObject_CallObject(my_python_callback,arglist);




 



         ;   Py_DECREF(arglist);



 



 



}




 



static PyObject *install_frame_hooker(PyObject
*dummy, PyObject *args){



 



int retVal =
0;



         ;   PyObject
*result = NULL;



             PyObject
*tobj;



         ;   



 



    if
(!PyArg_ParseTuple(args, "O:set_callback", &tobj)) 



       
return NULL;



    



    // make sure
second argument is a function



    if
(!PyCallable_Check(tobj)) {



       
PyErr_SetString(PyExc_TypeError, "Need a callable object!");




    }



         ;   Py_XINCREF(tobj);
/*add a reference to the new callback instance*/



         ;   Py_XDECREF(my_python_callback);

/*dispose of previous callback instance */




         ;   my_python_callback
= tobj; ;       /*save reference to new
callback instance */




         ;   



         ;   Py_INCREF(Py_None);



         ;   result
= Py_None;



         ;   /*now
this method must call the camera's SDK InstallFrameHooker to install 



         ;   the
C++ FrameHooker - note that 0 is raw data, 1 is bmp data */




         ;              ; 



         ;   retVal
= BUFUSB_InstallFrameHooker(0, FrameCallBack);




 



         ;   return
result;




}




 



static PyObject
*start_frame_grab(PyObject *self, PyObject *args){



         ;   //starts
grabbing data




         ;   int
retVal = 0;




 



         ;   //start
frame grab will cause camera engine to call on the frame hooker (callback)
method to return camera data




         ;   retVal
= BUFUSB_StartFrameGrab(0x8888);      ;  



 



         ;   return
Py_BuildValue("i", retVal);



 



}




 



static PyMethodDef camera_ext_methods[]

= {



         ;   {"StartFrameGrab",
start_frame_grab, METH_VARARGS, "Start grabbing frames, specify the number
of frames to grab"},



         ;   {"InstallFrameHooker",
install_frame_hooker, METH_VARARGS, "Set the callback function to notify
caller everytime the camera engine gets a new frame";},




         ;   {NULL,
NULL}




};



 



 



void initcamera_ext(void)



{




    import_array();




   
Py_InitModule("camera_ext", camera_ext_methods);



}










  

  
  
   
     
    






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