[PyKDE] How to test if two PyQt instances wrap the same C++ object?

[Phil Thompson]

On Wednesday 22 October 2003 11:36 am, Gerard Vermeulen wrote:
> On Wed, 22 Oct 2003 10:56:33 +0100
>
> Phil Thompson <phil at riverbankcomputing.co.uk> wrote:
> > On Wednesday 22 October 2003 9:19 am, Gerard Vermeulen wrote:
> > > Hi,
> > >
> > > I have difficulty to translate this C++ idiom in Python:
> > >
> > > bool Plot::eventFilter(QObject *object, QEvent *e)
> > > {
> > >     if ( e->type() == QEvent::Resize )
> > >     {
> > >         const QSize &size = ((QResizeEvent *)e)->size();
> > >         if ( object == (QObject *)axis(yLeft) )  // HOW TO THIS IN
> > > PYTHON? {
> > > 	// ...
> > >         }
> > >     }
> > >
> > >     return QwtPlot::eventFilter(object, e);
> > > }
> > >
> > > Of course I could write for PyQwt a function:
> > >
> > > qwt.compareCPlusPlusPointers(SuperObject, DerivedObject)
> > >
> > > but if it is really needed, it belongs in PyQt.
> >
> > Have you tried the obvious and it doesn't work?
> >
> > PyQt keeps a map of all C++ pointers and Python instances that it knows
> > about. When it wraps a C++ pointer it first checks if it already knows
> > about the pointer (while doing a bit of type checking). If it does then
> > it just returns a new reference to the existing Python instance. In other
> > words...
> >
> >     if object is axis(yLeft):
> >
> > ...should work. However...
> >
> > The "bit of type checking" deals with the common case where PyQt first
> > wraps a C++ pointer with a more specific type (eg. QLabel) and then is
> > asked to wrap it as a less specific type (eg. QWidget). It *doesn't*
> > handle the less common case (eg. the code above) when it sees the less
> > specific type first (QObject) and the more specific type second (whatever
> > axis() returns).
> >
> > The code to change is sipOMFindObject() in siplib/objmap.c. In SIP v4
> > change the single call to PyType_IsSubtype() to...
> >
> >         if (PyType_IsSubtype(w -> ob_type,&type -> super.type) ||
> >             PyType_IsSubtype(&type -> super.type,w -> ob_type))
> >                 return w;
> >
> > (I think the SIP v3 change is slightly more complicated.)
> >
> > Let me know if that works.
>
> Oops, not yet ready to try SIP-v4 on PyQwt, yet. And I also have Qwt
> duties tonight :-).  But I'll try to give it a try :-)

Actually the corresponding change in SIP v3 is obvious to someone of your 
abilities. The change will be in tonight's snapshots anyway.

Phil