Could something like this support forward declarations without the hackish use of strings?
On Sun, 21 May 2017 at 12:01 justin walters <walters.justi...@gmail.com> wrote: > 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 > -- Oliver My StackOverflow contributions My CodeProject articles My Github projects My SourceForget.net projects -- https://mail.python.org/mailman/listinfo/python-list
