Python 3, super.__del__()

Question

I have a __del__ method in a class I've defined, to delete some C++ objects created by calling C++ new in a ctypes interface. I want to delete these objects when an instance of my class is destroyed. I have a fragment of the class shown here:

class Graph(QtCore.QObject):
    def __init__(self):
        super().__init__()
        #list of objects created by calls to ctypes to create pointers to C++ objects which are instantiated with C++ new 
        self.graphs = []

    def __del__(self):
        print("in delete method")
        for graph in self.graphs:
            # call the C++ delete to free the storage used by this graph
            myctypes.graphDelete(graph)
        super().__del__()

When an instance of my Graph class is deleted, the __del__ method is called and I see my print statement and when I set a breakpoint in the destructor method in the C++ code, as expected, it deletes the object. However, when my __del__ method calls super().__del__(), I get the error message:

super().__del__()
AttributeError: 'super' object has no attribute '__del__'

How do I ensure that the parent class (QtCore.QObject) is deleted if I define my own __del__ method in the child class or will the parent class be deleted automatically?

Answer 1

The role of __del__ is not to delete the object: it is called before the object is automatically deleted. Therefore it's fine if your parent class doesn't define __del__. Feel free not to call super().__del__() if it's bugging you.

For the record, the reason why objects don't have a default __del__ is that objects with __del__ were not garbage collected in case of reference cycles (until Python 3.4). For more information, read the documentation for gc.garbage in Python 3.3 and for gc.garbage in Python 3.4.