OK, this isn't actually part of my SOLID Principles series (always a pity when your best content is a youtube link) but a response to Ryan's article on Los Techies.  I've not really got my head around the way that unit testing works in python, but the I get that absolutely everything is being overrideable on an instance or class basis affects the approach. Let's talk about Ryan's list.  Now, he argues that Python offers alternatives for the interface segregation principle, open/closed principle, and the dependency inversion principle.  I'm going to argue that the principles are actually the same,...