The same way you can parse a string into an integer and it knows you got an either[integer, err].

So it doesn't, and it's not about the type system. Any decode operation in python 3 raise an exception or return string.

It's about the runtime error handling making it mandatory to deal with the error and won't let you panic at run time for this specific error.

I'm sorry you don't see exceptions as part of a type system yet.