Question: How for force deletion of a child QObject?

[rainman110]

Lets assume, I have a object hierarchy

Parent
|--> child

Parent is currently managed by C++ and thus child as well. Now lets assume a python function get_child, that returns the child.

Now I'd like to make PythonQt the owner of the returned child object, meaning that when the returned object is deleted by python, also the child should be deleted and removed from its parent automatically. Here's the example to be more precise

parent = get_parent()
child_obj = get_child(parent, own=True)

del child_obj # Now, child should be removed from parent

The function PythonQtInstanceWrapper_deleteObject is used as a destructor of QObject-type python objects. Inside this function, the code to free the underlying QObject is the following

pythonqt/src/PythonQtInstanceWrapper.cpp

Lines 105 to 109 in 3cc771c

	if (force || self->_ownedByPythonQt) {
	if (force || !self->_obj->parent()) {
	delete self->_obj;
	}
	} else {

As you can see, the existence of a parent ensures, that the child is not deleted, even if PythonQt has ownership. This makes sense in most cases. This destructor function though has a force argument, which I'd like to use. How can I make sure, that the force argument is set to true?

A hint in the PythonQt code is

pythonqt/src/PythonQtInstanceWrapper.cpp

Lines 344 to 356 in 3cc771c

	PyObject *PythonQtInstanceWrapper_delete(PythonQtInstanceWrapper * self)
	{
	PythonQtMemberInfo deleteSlot = self->classInfo()->member("py_delete");
	if (deleteSlot._type == PythonQtMemberInfo::Slot) {
	// call the py_delete slot instead of internal C++ destructor...
	PyObject* resultObj = PythonQtSlotFunction_CallImpl(self->classInfo(), self->_obj, deleteSlot._slot, nullptr, nullptr, self->_wrappedPtr);
	Py_XDECREF(resultObj);
	} else {
	PythonQtInstanceWrapper_deleteObject(self, true);
	}
	Py_INCREF(Py_None);
	return Py_None;
	}

which forces object destruction, if deleteSlot._type != PythonQtMemberInfo::Slot. What does this mean? Is there any way to exploit this?

[usiems]

If I read this correctly this else branch should be used automatically if you didn't specify a "py_delete" slot method in your QObject.
(You can specify a py_delete method to handle deletion yourself.)

[rainman110]

Do you have any example how to use py_delete? So instead of calling the desctructor of the QObject, a custom py_delete slot is called to intercept the deletion?

But according to the code, without a "py_delete" slot, the branch PythonQtInstanceWrapper_deleteObject(self, true); is called with force==true. I though did not observe, that deletion has been forced.