I'm not sure I get his point. Is it that "A member (field) of a class is not a proper interface"? In Python, that's not really true, since he could have used a

I'm not sure I get his point. Is it that "A member (field) of a class is not a proper interface"? In Python, that's not really true, since he could have used a property and kept his first design. How is that significantly different from his final solution?