Actually it's just checking the types at runtime, nothing much 'static' about it. This is pretty much the antithesis of duck typing, in fact. I could see it being useful, but I could also see it leading to confusion for people who expect Python's usual duck-typing behaviour when they pass their own types into a function.

Whoops you subclassed from a type for which this function has a multimethod defined? Gonna do something different.

On the other hand, in non-trivial programs there _are_ certainly occasions when you need to check the type, so using an elegant method like this isn't a bad compromise.