Yeah, static type checkers won't like it regardless.
On Tue, Dec 8, 2020 at 6:39 PM Paul Bryan <[email protected]> wrote:
> It appears that when from future import __annotations__, a type hint
> annotation derived from a closure loses scope.
>
> Simplistic example:
>
> Python 3.9.0 (default, Oct 7 2020, 23:09:01)
>
> [GCC 10.2.0] on linux
>
> Type "help", "copyright", "credits" or "license" for more information.
>
> >>> def make_a_class(data_type):
>
> ... class Foo:
>
> ... def put_data(self, data: data_type):
>
> ... self.data = data
>
> ... return Foo
>
> ...
>
> >>> import typing
>
> >>> foo = make_a_class(str)()
>
> >>> typing.get_type_hints(foo.put_data)
>
> {'data': <class 'str'>}
>
> >>>
>
>
> If I add a single import to the top, it breaks:
>
> Python 3.9.0 (default, Oct 7 2020, 23:09:01)
>
> [GCC 10.2.0] on linux
>
> Type "help", "copyright", "credits" or "license" for more information.
>
> *>>> from __future__ import annotations # added this line*
>
> >>> def make_a_class(data_type):
>
> ... class Foo:
>
> ... def put_data(self, data: data_type):
>
> ... self.data = data
>
> ... return Foo
>
> ...
>
> >>> import typing
>
> >>> foo = make_a_class(str)()
>
> >>> typing.get_type_hints(foo.put_data)
>
> Traceback (most recent call last):
>
> File "<stdin>", line 1, in <module>
>
> File "/usr/lib/python3.9/typing.py", line 1386, in get_type_hints
>
> value = _eval_type(value, globalns, localns)
>
> File "/usr/lib/python3.9/typing.py", line 254, in _eval_type
>
> return t._evaluate(globalns, localns, recursive_guard)
>
> File "/usr/lib/python3.9/typing.py", line 493, in _evaluate
>
> eval(self.__forward_code__, globalns, localns),
>
> File "<string>", line 1, in <module>
>
> NameError: name 'data_type' is not defined
>
> >>>
>
>
> I don't see how I can supply the closure scope as localns to
> get_type_hints. Any suggestions? Is constructing a
> (dynamically-type-annotated) class in a function like this an anti-pattern?
>
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--
--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/>
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