[PyKDE] embedding python widgets in C++ app

[Patrick Stinson]

On 1/22/07, Phil Thompson <phil at riverbankcomputing.co.uk> wrote:
> On Monday 22 January 2007 9:21 am, Patrick Stinson wrote:
> > oops, I think the title is backwards. I will send the author an email.
> > I am trying to embed a python widget in a C++ application, where he is
> > trying to access his C++ app code from his python code.
> >
> > I decided to manually import a module with a factory function, call
> > that factory function from C++ and convert the python object to a
> > QWidget * using sipConvertToInstance. After doing this, I have a few
> > questions:
> >
> > What should the transfer object be as passed to sipConvertToInstance?
> > I'm a little confused about the wording in the documentation, and
> > sipTransferObj is automatically included if you are using this in a
> > sip file.
>
> It depends on what you are going to do with the C++ instance (when is the dtor
> going to be called) and it's Python object (when is it going to be garbage
> collected). Do you want the C++ instance to outlive the Python object?

Well, I suppose it would crash if the C++ instance outlived the python
object since the widget is defined in python. Is that right, or am I
turned around?

>
> > How are you supposed to statically link the PyQt libraries if you then
> > lose the PyQt4 package, which initQtGui() expects to import QtCore
> > from? initQtCore() works fine but initQtGui() fails looking for
> > PyQt4.QtGui.
>
> PyQt modules are modules - they are not libraries. You do not link against
> them. You can configure them as builtin modules, just like any other module.

Hmm ok. So you only recommend compiling them into a custom
interpreter? Does this make sense with a primarily C++ app, with it's
own entry point and source tree?

Does that mean that linking against libpython.a, or the resulting
python framework on mac will include the pyqt modules as builtins?
Considering pyqt modules are nomral pyhton modules I should probably
just read mac-related docs for deploying C++ app bundles with embedded
custom interpreters. That is the problem I'm facing afterall..

I remember seeing an old document by you on how to build a custom
interpreter with the pyqt3 sources. I guess I could follow those
instructions again...

>
> > Any comments on the following code?
> >
> >   char nameBuf[2048];
> >   strcpy(nameBuf, moduleName);
> >   PyObject *module = PyImport_ImportModule(nameBuf);
> >   if(module)
> >     {
> >       PyObject *_create = PyObject_GetAttrString(module, "_create");
> >       if(_create)
> >         {
> >           if(PyCallable_Check(_create))
> >             {
> >               PyObject *sipPy = PyObject_Call(_create,
> > Py_BuildValue("()"), NULL);
> >               if(sipPy)
> >                 {
> >                   int iserr = 0;
> >                   QWidget *widget = reinterpret_cast<QWidget
> > *>(sipConvertToInstance(sipPy, sipClass_QWidget, NULL, SIP\
> > _NO_CONVERTORS, 0, &iserr));
> >                   if(iserr == 0 && widget)
> >                     {
> >                       widget->show();
> >                       qDebug("GOT WIDGET %p", widget);
> >                       ret = widget;
> >                     }
> >                   else
> >                     qWarning("could not sip => widget");
> >                 }
> >               else
> >                 qWarning("error in _create return (%p)", sipPy);
> >             }
> >           else
> >             qWarning("error \"_create\" is not callable");
> >           Py_DECREF(_create);
> >         }
> >       else
> >         qWarning("no attribute \"_create\"");
> >     }
> >   else
> >     qWarning("no module \"pktest\"");
>
> Obviously you are leaking the sipPy and widget instances.
>
> The above code has to be part of a SIP generated module that %Imports
> PyQt4.QtGui. The SIP API can only be called from SIP generated modules.

Well, the function above would return the widget instance to code that
would call QWidget::setParent(). The only goal is to write a widget in
python and use it in my C++ app. If there is a better way..

>
> Phil
>
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>


-- 
Patrick Kidd Stinson
http://www.patrickkidd.com/
http://pkaudio.sourceforge.net/
http://pksampler.sourceforge.net/