I think this would just perpetuate misunderstanding about how things work. You're proposing to make it so that changing the body of the function (in particular, removing `y: T`) would affect the interpretation of the type annotation. That's just wrong.
On Wed, Feb 3, 2021 at 12:47 PM Caleb Donovick <donov...@cs.stanford.edu> wrote: > > Here we want to know what the 'C' refers to in g's annotations. But g's > closures are no help (unless g's body were to also reference C, which is > not likely in typical code). > > I understand the limitation. I was proposing changing > https://github.com/python/cpython/blob/3.9/Lib/typing.py#L1431-L1433 to > use the `nonlocal_vars` instead of `globalns` for the default localns (or > possibly a chainmap of the two). I agree that it may only work on a small > fraction of code but the performance cost seems pretty minimal especially > for a function like `get_type_hints`, so why not? But I trust judgement, > if you think that creating an apparent inconsistency around when > `get_type_hints` will work and when it won't is not worth being able to > resolve a few extra cases it probably isn't. > > - Caleb Donovick > > On Wed, Feb 3, 2021 at 8:55 AM Guido van Rossum <gu...@python.org> wrote: > >> Sadly this won't work, because the annotations are "evaluated" (or not) >> in the surrounding scope, not in the function's scope. Example: >> ``` >> >>> def f(a: int): >> ... class C: pass >> ... def g(b: C): pass >> ... return g >> ... >> >>> g = f(1) >> >>> g.__annotations__ >> {'b': 'C'} >> >>> g.__closure__ >> >>> >> ``` >> Here we want to know what the 'C' refers to in g's annotations. But g's >> closures are no help (unless g's body were to also reference C, which is >> not likely in typical code). >> >> --Guido >> >> On Tue, Feb 2, 2021 at 6:10 PM Caleb Donovick <donov...@cs.stanford.edu> >> wrote: >> >>> The discussion around PEP 649 got me thinking about what I believe is >>> the largest downside to PEP 563: the inability to evaluate annotations >>> created with closures. While this is in general unavoidable, if the type >>> is ever referenced in an annotated function (including as an annotation) it >>> should be resolvable via `__closure__`. >>> >>> For example: >>> ``` >>> from __future__ import annotations >>> import typing >>> def gen(T): >>> def f(x: T): >>> y: T = ... >>> return f >>> >>> f = gen(int) >>> nonlocal_vars = { >>> var : cell.cell_contents >>> for var, cell in zip(f.__code__.co_freevars, f.__closure__) >>> } >>> assert typing.get_type_hints(f, localns=nonlocal_vars) == {'x': int} >>> ``` >>> >>> I would just open a PR to have `get_type_hints` attempt to resolve >>> closure variables by default. However, this would require an update to PEP >>> 563 and I don't know what the protocol is there. >>> >>> - Caleb Donovick >>> _______________________________________________ >>> Python-Dev mailing list -- python-dev@python.org >>> To unsubscribe send an email to python-dev-le...@python.org >>> https://mail.python.org/mailman3/lists/python-dev.python.org/ >>> Message archived at >>> https://mail.python.org/archives/list/python-dev@python.org/message/L2XH2EIFCEPT5DQRPRFR6WYEM6M2LM2V/ >>> Code of Conduct: http://python.org/psf/codeofconduct/ >>> >> >> >> -- >> --Guido van Rossum (python.org/~guido) >> *Pronouns: he/him **(why is my pronoun here?)* >> <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/> >> > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
_______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/QHOB5JXKRVH4MI3JARJANUMDR5HLHLNH/ Code of Conduct: http://python.org/psf/codeofconduct/
