None of the above fixed my problem. Apparently sometimes Python doesn't like the subclass to inherit @properties. See this screenshot:

parent_graph used to be an @property and the same analogous error you see displayed in the picture occured. Now I made it into a regular method. So now it gets past that error and moves onto the next uninherited @property which is ambient_space. So now you can imagine what I have to do: take away @property's in practically my whole project.

Arrow is using single inheritance from base class Base which in turn singly inherits from QGraphicsObject. I am definitely calling the super().__init__() appropriately.