> In Python it isn't implicit, but it's still shared state, and so still hard to test and maintain. You can't test the `f` in your example without having to pass in the whole big bundle of state that self tends to be, even if you do so explicitly.

cies said structs were ok, what's the difference in this regard? 'Shared state' doesn't usually refer to explicitly passing a data structure into a function as an argument; it's operating on shared state only in the same way that any function which takes for example a string or a hash does.