Construct class from superclass instance

Question

So you have some function, say Gtk.Builder.get_object(), which returns some widget. In our case a Gtk.Window().

I have a subclass of Gtk.Window() which adds some signal handlers.

class Window(Gtk.Window):

Is it possible to use the widget returned by Gtk.Builder.get_object() to construct Window()? I think it should be using __new__() or something, but I can't figure it out.

Answer 1

I think using __new__ is exactly what you want to be doing. If you can set the __class__ attribute of the superclass instance you're getting to the subclass, you should be all set.

Here's what I think you need:

class Window(Gtk.Window):
    def __new__(cls, *args, **kwargs):
        self = Gtk.Builder.get_object()
        self.__class__ = cls
        return self

Python should detect that the value that was created by __new__ is an instance of the class (thanks to the __class__ value), then it will call __init__ and other methods as appropriate.