datetime.tzinfo is abtract

[sobolevn]

This class is not marked as abstract, but it is documented:

Abstract base class for time zone info classes.
Subclasses must override the name(), utcoffset() and dst() methods.

Source: https://github.com/python/cpython/blob/f6b1e4048dc353aecfbfbae07de8212900632098/Lib/datetime.py#L1222-L1243

[sobolevn]

I was following return types from https://docs.python.org/3/library/datetime.html#datetime.timezone

[sobolevn]

ZoneInfo can return None because of https://github.com/python/cpython/blob/f6b1e4048dc353aecfbfbae07de8212900632098/Lib/zoneinfo/_zoneinfo.py#L418

[sobolevn]

dateutil source: https://github.com/dateutil/dateutil/blob/7c5c98959bd0e9eea3c55fdf78bef3ae5b8c995e/src/dateutil/tz/_common.py#L149

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sphinx (https://github.com/sphinx-doc/sphinx)
+ sphinx/builders/gettext.py:191:7: error: Cannot instantiate abstract class "LocalTimeZone" with abstract attribute "tzname"  [abstract]

[sobolevn]

Example in Sphinx is technically correct:

class LocalTimeZone(tzinfo):
    def __init__(self, *args: Any, **kwargs: Any) -> None:
        super().__init__(*args, **kwargs)
        self.tzdelta = tzdelta

    def utcoffset(self, dt: Optional[datetime]) -> timedelta:
        return self.tzdelta

    def dst(self, dt: Optional[datetime]) -> timedelta:
        return timedelta(0)


ltz = LocalTimeZone()

LocalTimeZone misses tzname method definition.
Link: https://github.com/sphinx-doc/sphinx/blob/c1f2a52d5d97f874d84e4d5421c99a566242af6b/sphinx/builders/gettext.py#L191

I will send a PR.

[hauntsaninja]

Do we need to add the metaclass, since runtime doesn't have it? mypy allows for checking abstractmethod without metaclass

[sobolevn]

Do we need to add the metaclass, since runtime doesn't have it? mypy allows for checking abstractmethod without metaclass

Yes, we sometimes need this.

Please, take a look at this error:

error: not checking stubs due to mypy build errors:
stdlib/zoneinfo/__init__.pyi:12: error: Class zoneinfo.ZoneInfo has abstract attributes "dst", "tzname", "utcoffset"
stdlib/zoneinfo/__init__.pyi:12: note: If it is meant to be abstract, add 'abc.ABCMeta' as an explicit metaclass

[sobolevn]

Basically, ABCMeta metaclass is an explicit marker that some class is indeed abstract. That it is not just a missing method by accident.

[hauntsaninja]

Oh interesting, didn't realise there was this stub-only check: https://github.com/python/mypy/blob/5e1e26eba15b43449bdce4010bf16d160d3ec505/mypy/semanal_classprop.py#L97

[AlexWaygood]

We need the metaclass change in dateutil, but I don't think we need the metaclass change for datetime.tzinfo itself