You got me curious so I looked it up. Apparently in Cpython 'Union' is not a class itself, but is a special object of type _SpecialForm, which is created by usi

You got me curious so I looked it up. Apparently in Cpython 'Union' is not a class itself, but is a special object of type _SpecialForm, which is created by using _SpecialForm as a decorator on a function 'Union' which returns the actual union type given a set of parameters. Interestingly _SpecialForm uses a mixin _Final to prevent subclassing. This mixin is made using __init_subclass__