Collin Funk <[email protected]> writes:
>> 'from __future__ import annotations', available since Python 3.7 [1],
>> allows older Pythons to ignore type-hint syntax sophistications brought
>> by newer Pythons.
>>
>> So if Python 3.7 is acceptable as a minimum version (it seems available
>> in the distro releases you mention), you would be able to start using
>> this union syntax.
>
> I remember having to use the __future__ import. I guess I no longer
> have to now that Debian Stable has Python 3.11.
>
> Do you happen to know if 'from __future__ import annotations' allows
> for the use of 'TypeX | TypeY' union syntax with Python 3.7?
Yes, 'TypeX | TypeY' was what I was referring to above with "syntax
sophistications brought by newer Pythons". Demonstration:
Python 3.7.17+ (tags/3.7:0f56adb8d7, Mar 1 2024, 08:50:56)
[GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def foo(s: str | list[str]) -> str | list[str]:
... return s
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'type' object is not subscriptable
>>> from __future__ import annotations
>>> def foo(s: str | list[str]) -> str | list[str]:
... return s
...
>>> foo("hello")
'hello'
So Pythons ≥3.7 can import 'annotations' from '__future__', and that
lets them gloss over newer annotation constructs they do not understand…
unless we actively tries to evaluate them:
>>> from typing import get_type_hints
>>> get_type_hints(foo)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/legouguec/src/python/3.7/Lib/typing.py", line 1013, in
get_type_hints
value = _eval_type(value, globalns, localns)
File "/home/legouguec/src/python/3.7/Lib/typing.py", line 263, in
_eval_type
return t._evaluate(globalns, localns)
File "/home/legouguec/src/python/3.7/Lib/typing.py", line 467, in
_evaluate
eval(self.__forward_code__, globalns, localns),
File "<string>", line 1, in <module>
TypeError: 'type' object is not subscriptable
> I was
> under the impression that it was added for 3.10 [1]. I think that for
> compatibility with older versions you could write:
>
> def func(var) -> Union[int, str]:
>
> instead of:
>
> def func(var) -> int | str
Right, that's another route you can go if (a) the linters you expect to
use run Pythons <3.10, so they are subject to the above caveat, and/or
(b) you expect to call typing.get_type_hints in your own scripts
(e.g. GDB's DAP server uses that to sanity-check client requests) and/or
(c) you (collective, as a project) find it more legible.
> [1] https://docs.python.org/3/library/typing.html#typing.Union
>
> Thanks,
> Collin
