In the <BaseWidget._setup> method, <master> is evaluated as a Boolean (when Tkinter attempts to find a parent for the widget). I think it should really be evaluated against <None>, seeing as that is the default <master> keyword argument value for most widgets. I ran into problems with this when making a container widget class that inherited from the <Canvas>, then implementing the <__len__> magic method. When the length was zero the widget would evaluate as false, which would prevented me from packing widgets inside my container widget.

I attached a revised version of the method.