On Sun, May 21, 2017 at 2:38 AM, Chris Angelico <ros...@gmail.com> wrote:
> On Sun, May 21, 2017 at 7:29 PM, bartc <b...@freeuk.com> wrote: > > > > They might be /created/ at runtime, but it's a pretty good bet that the > name > > A in this declaration: > > > > class A... > > > > is the name of a class. The question in Python, as always, is whether an > A > > used as the name of a type in a type, is still this same A. And > presumably > > such a type hint can precede the declaration of A. > > > > In fact the declaration of A might be in a different module from its use > in > > a type hint, which means that, in the CPython byte-code compiler anyway, > it > > is not visible at compile-time, when type hints could best be put to good > > effect. > > That isn't a problem - mypy follows imports. It'd be pretty useless if > it didn't :) > > > Furthermore, both A, and the type-hinting code, might be conditional. So > > that on Tuesdays, A is a class, the rest of the week it's the name of a > > module. > > Or, more plausible example: on platforms that have a system-provided > source of entropy, random.random is an instance of SystemRandom, but > on those that don't, it's an instance of DeterministicRandom with an > arbitrarily-chosen seed. The two will have slightly different APIs. > > > Python doesn't make things easy. > > Python makes things flexible, which has a cost. > > ChrisA > -- > https://mail.python.org/mailman/listinfo/python-list > Perhaps a good way to distinguish between a class that can be used as a type and a class that cannot be used as a type would be to require some sort of dunder method be defined on the type class. At first I was thinking `__type__`, but then I remembered that's already in use. maybe something as simple as `__hint__`. That or only allow classes that inherit from `type` to be used in type annotations. I'm just spit balling ideas here. -- https://mail.python.org/mailman/listinfo/python-list
