dates.py syntax incompatibility with python versions older than 3.10

[MandarinoMcZumo]

Overview Description

Python syntax version incompatibility. The module dates.py applies the 3.10 union syntax. That is not compatible with older versions of python that the package should support. 3.10:

if TYPE_CHECKING:
    from typing_extensions import Literal, TypeAlias
    _Instant: TypeAlias = datetime.date | datetime.time | float | None
    _PredefinedTimeFormat: TypeAlias = Literal['full', 'long', 'medium', 'short']
    _Context: TypeAlias = Literal['format', 'stand-alone']
    _DtOrTzinfo: TypeAlias = datetime.datetime | datetime.tzinfo | str | int | datetime.time | None

older:

if TYPE_CHECKING:
    from typing_extensions import Literal, TypeAlias
    _Instant: TypeAlias = Union[datetime.date, datetime.time, float, None]
    _PredefinedTimeFormat: TypeAlias = Literal['full', 'long', 'medium', 'short']
    _Context: TypeAlias = Literal['format', 'stand-alone']
    _DtOrTzinfo: TypeAlias = Union[
        datetime.datetime, datetime.tzinfo, str, int, datetime.time, None]

[akx]

I'm not sure if there's an actual problem here – Mypy supports that syntax regardless of the Python version it's being run on, and that code will never be evaluated at runtime since it's in a if TYPE_CHECKING block?

[akx]

Closing since there is no additional information and we know Babel runs fine on versions older than 3.10 (for the time being).