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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