Ben Finney <ben+pyt...@benfinney.id.au> writes: > There's a big overlap because most classes are also types -- but not > the other way around! E.g. Any is a type but not a class (you can > neither inherit from Any nor instantiate it), and the same is true > for unions and type variables. […]
> As a Bear of Little Brain, this leaves me clueless. What is the > distinction Guido alludes to, and how are Python classes not also types? I thought I understood Guido's explanation but maybe I missed something. Let C be a class, maybe defined by a class statement or maybe a builtin like "int". You can make an instance of C the usual way: x = C() And you can have a type annotation that says function f expects an arg that is an instance of C: def f(x : C) -> int: ... You might alternatively write a function whose arg must be either an int or a string: def f(s : Union[int, str]) -> int : ... or (I think, I haven't tried it) you can equivalently bind that type to a variable: T = Union[int, str] def f(s : T) -> int : ... The point here is that T is a type but it is not a class. You can't instantiate T by saying x = T() and expecting to get back some value that is (indeterminately) an int or a string. That is, there's stuff (like instantiation) that you can do with types that happen to be classes, but there are also types that aren't classes. -- https://mail.python.org/mailman/listinfo/python-list
