[PyQt] A question regarding SIP

Ravi kumar ravi.kumar.039 at gmail.com
Mon Feb 22 02:18:01 GMT 2010


I am learning SIP, and have a small question regarding it. Let me
explain the situation :

I have a small test library written in C++. It is made up of two
files, test.hpp and test.cpp
with declarations and implementation respectively. There is a
particular declaration that
goes like this :

namespace Test {

	class KlassProcessor {

		virtual void process2 (...) {

I successfuly written a python extension using SIP, and the extension
is named : test
So, to use KlassProcessor, one may do like this in python :

from test import Test
kp = Test.KlassProcessor ()
kp.process2 (...)           # ... are arguments, not part of my problem

Now after that what i did is made a C++ program with python embedded
in it : embed
Also, i made a python script that imports 'test' and use it, named
    : etest

now 'embed' is supposed to import 'etest' and use it.

'etest' has a function : 'process',

which takes an argument which is supposed to be an instance of
and it calls its 'process2' member function, so the contents of
'etest.py' goes like this :

def process (kp) :
	kp.process2 (...)

now back inside my C++ code of 'embed' program, i imported 'etest',
and then using
PyObject_GetAttrString, i got the pointer to 'process' function in it.

But also, i have made a new class in that C++, which inherits from
Test::KlassProcessor :

class MyProcessor : Test::KlassProcessor {
	virtual void process2 (...) {
		... // redefined

I created an instance of this class, and sent it as argument to the
'process' function of
'etest', using the following code :

// Creating instance
MyProcessor* processor = new MyProcessor ();

// Getting proper sipWrapperType
const sipTypeDef* kpTypeDef     = sipFindType ("Test::KlassProcessor");
PyTypeObject*     kpTypeObject  = sipTypeAsPyTypeObject (kpTypeDef);
sipWrapperType*   kpWrapperType = reinterpret_cast<sipWrapperType*>

// Wrapping up C++ instance
PyObject* pyProcessor = sipConvertFromInstance (processor, kpWrapperType, NULL);

// Getting pointer to 'etest.process' function
PyObject* process = PyObject_GetAttrString (etest, "process");

// Finally calling 'process'
PyObject* argTup = Py_BuildValue ("(O)", pyProcessor);
PyObject_Call (process, argTup, NULL);
Py_XDECREF (argTup);

What is happening there that the 'process' function is calling the 'process2'
of the argument. But rather than the 'process2' of my inherited 'MyProcessor',
the 'process2' of its parent class 'Test::KlassProcessor' is being called.

I know that i can very well write an extension of MyProcessor and be done with
this problem. But i was just curious that is there any way to pass inherit
the SIP-extended class in C++ and then using its instance from python ?

Last but not least, i would like to write some examples on using SIP
which might help beginners learning it. is it ok if i add it into the wiki at
http://www.diotavelli.net/PyQtWiki ? I am asking this bcoz almost all
the tutorials there are regarding PyQt or PyKDE... so maybe there is some
other proper place to post them..

Thanks in advance to anyone who took the time to read my problem :)

And finally thanks for SIP :)

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