On Fri, 4 May 2012 15:25:10 +0200, Jens Thoms Toerring <j...@toerring.de> wrote: > On Fri, May 04, 2012 at 01:42:11PM +0100, Phil Thompson wrote: >> On Fri, 4 May 2012 14:33:10 +0200, Jens Thoms Toerring <j...@toerring.de> >> wrote: >> > I have a C++ class SIP-wrapped with the '/Abstract/' >> > annotation, Thus Pyton just has a pointer to instances of >> > this class (and ownership is with C++). Now, at a certaind >> > point I would like to make the Python wrapper object point >> > to a different instance (of the same class). Finding the add- >> > ress of the Python object is simple using sipGetPyObject(). >> > But is there some way make that Python object refer to a dif- >> > ferent of my C++-objects? I guess that there's some pointer >> > to my C++ object in that Python object that just need to be >> > modified to point to the new instance of the C++ class. I've >> > been going through all of the dicumentation several times but >> > haven't found anything that looks as if would do something >> > like that. And, of course, I wouldn't like to mess with un- >> > documented features of the SIP-wrapper, resulting in every- >> > thing breaking with the next SIP release;-) >> >> There is no supported way of doing this. > > Thank you. Bit of a pity. Guess I'll have to find some other > way of dealing with this... > > In case you're interested in the background here's an attempt > to explain what I'm doing. Consider you have a class for dir- > ectories and a class for files in that directory. Also assume > that for some reasons (see below) the ownership must remain > with C++. Now the directory class has a method to delete the > directory. Thus the C++ object for the directory object as > well all the objects for the files in the directory get de- > leted. No problem with C++ - I simply document that if you > have used the delete() method using the directory object and > all the file objects derived from it can't be used anymore - > C++ programmer are used to such things. But Python still has > the wrapper objects with the pointers and if the user tries > to use them afterwards the whole script will (in the best of > all cases) crash. That doesn't look very "pythonic" to me - > I guess a Python programmer will expect the script to abort > with an exception, explaining about the errors of his way. > Thus I would like to "redirect" the Python wrapper objects > to a new C++ objects that, when used, throw an exception > (and transfer ownership for them to Python, so they get > deleted when Python garbage-collects the wrapper objects). > > If you wonder why I need to keep the ownership to C++ there > are two reasons (the actual stuff I do isn't about directories > and files, it's just simpler to visualize it that way): these > objects have a lot of data (several hundreds of MB) and making > copies of them simply would require too much memory.
What's that got to do with ownership? Ownership is simply who has responsibility for calling the dtor. > Moreover, > under some circumstanes these objects must be immutable - and > Python doesn't seem to have C++'s notion of const-ness. > > Best regards, Jens Phil _______________________________________________ PyQt mailing list PyQt@riverbankcomputing.com http://www.riverbankcomputing.com/mailman/listinfo/pyqt
