PythonQt Wrapper Reference counting

[Joerg Kreuzberger]

Hi!

I have a question regarding reference counting.
I have a C++ object, owned by my app. In PythonQt i have created a wrapper, so i call
registerClass("PyClassName","","", PythonQtCreateObject<cppwrapper>)</cppwrapper>

The class comes into python via another c++ object. There is no wrapper to create or delete it from python.
In python i call
b1 = MyObject.get()

b1 shows to my c++ object (adress)
if i now call b1 = None, i get no hint it is not used any more
how can i detect this?
Is this the last parameter in registerCppClass for ( PythonQtShellSetInstanceWrapperCB*)
or is there a special callback in the wrapper required?
the delete_PyClassName slot in the wrapper is not called ( i assume because not Object created in python)

A long time ago thread from 2010 stated it could also be not possible?

Any hints welcome :-)

[Florian Link]

The default ownership of returned objects is C++, so your object is not deleted by Python, just the wrapper to it. If your get() method returns a new object and you want Python to delete it, you can use the ownership templates in PythonQt.h

http://pythonqt.sourceforge.net/classPythonQtPassOwnershipToPython.html#aaad0d16be54de03dbd53c5184f1318eb

the templates don't do anything, but tell PythonQt that a returned pointer should change ownership.

The shell callback is something else, it is used to set the wrapper object on the shell class (the shell class allows deriving a class in Python and implementing the virtual methods in Python.

[Joerg Kreuzberger]

Ok, understand.

In my case i do not give the ownership to python currently, but i could. Then it would get deleted, and so my destructor is called.
http://pythonqt.sourceforge.net/Developer.html in the section with ownership management the return type of my MyObject.get() slot could do this

Question is if this is not the case, so if i do not WANT the object to be deleted, but used in python, CAN my object be INFORMED that the wrapper object is deleted? Or would this be a new feature?

[Florian Link]

No, there is no such mechanism. PythonQt could have a callback to notify you when an object wrapper is deleted, but it would not know where the object came from.

[Joerg Kreuzberger]

Hmm, does not work as expected by myself.
The slot has now a return type of

PythonQtPassOwnershipToPython<PyBitView*> 

But the destructor of the PyBitView object is never called if i delete the object in python
Is there still a reference hold by the wrapper object?
I currently cannot find the source code line to start debugging on, perhaps you have an hint?
Started from PythonQtSlot call. The result seems to have the right flags.

[Florian Link]

Hm, does your wrapper have a destructor slot (I forgot how they are named, delete_XYZ)? Because that is what PythonQt will use to destroy it (otherwise it can't destroy it).

[Joerg Kreuzberger]

and this it was. Argh. i removed the slot BEFORE trying it with this PassOwnerShipStuff.
Many thanks!!!