Yes, it’s https://bugs.python.org/issue34776
--
Eric
> On Sep 27, 2018, at 12:05 PM, Ivan Levkivskyi <levkivs...@gmail.com> wrote:
>
> Do we have a b.p.o. issue about this? If no, then I would recommend to open
> one, so that we will not loose track of this.
>
> --
> Ivan
>
>
>
>> On Sat, 22 Sep 2018 at 16:32, David Hagen <da...@drhagen.com> wrote:
>> The new postponed annotations have an unexpected interaction with
>> dataclasses. Namely, you cannot get the type hints of any of the data
>> classes methods.
>>
>> For example, I have some code that inspects the type parameters of a class's
>> `__init__` method. (The real use case is to provide a default serializer for
>> the class, but that is not important here.)
>>
>> ```
>> from dataclasses import dataclass
>> from typing import get_type_hints
>>
>> class Foo:
>> pass
>>
>> @dataclass
>> class Bar:
>> foo: Foo
>>
>> print(get_type_hints(Bar.__init__))
>> ```
>>
>> In Python 3.6 and 3.7, this does what is expected; it prints `{'foo': <class
>> '__main__.Foo'>, 'return': <class 'NoneType'>}`.
>>
>> However, if in Python 3.7, I add `from __future__ import annotations`, then
>> this fails with an error:
>>
>> ```
>> NameError: name 'Foo' is not defined
>> ```
>>
>> I know why this is happening. The `__init__` method is defined in the
>> `dataclasses` module which does not have the `Foo` object in its
>> environment, and the `Foo` annotation is being passed to `dataclass` and
>> attached to `__init__` as the string `"Foo"` rather than as the original
>> object `Foo`, but `get_type_hints` for the new annotations only does a name
>> lookup in the module where `__init__` is defined not where the annotation is
>> defined.
>>
>> I know that the use of lambdas to implement PEP 563 was rejected for
>> performance reasons. I could be wrong, but I think this was motivated by
>> variable annotations because the lambda would have to be constructed each
>> time the function body ran. I was wondering if I could motivate storing the
>> annotations as lambdas in class bodies and function signatures, in which the
>> environment is already being captured and is code that usually only runs
>> once.
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