There's no reason you can't do this. Python has free functions. It was an intentional style choice to do it this way. You can also make a diagonalize function

There's no reason you can't do this. Python has free functions. It was an intentional style choice to do it this way. You can also make a diagonalize function that just calls the method if you like that style better, half of python's generic functions (e.g. len) just call methods anyways.