RFE: use zoneinfo instead of pytz

[kloczek]

Switch to standard zoneinfo module.
Below may help pydantic/pydantic-core@fd262933

[rbtcollins]

Whats the motivation?

[cjwatson]

I think there's something to be said for avoiding non-stdlib dependencies when they're not needed. pytz used to be one of the easiest ways to get hold of a timezone object, but that hasn't been the case for a while now.

That said, I don't know why this package would use zoneinfo, since (unlike pydantic-core) it only uses pytz.UTC. datetime.timezone.utc is simpler and should be good enough.

[rbtcollins]

zoneinfo was introduced in 3.11; 3.8 is still receiving security fixes; I'm not super keen with Python with depending on the latest and greatest - have had significant pain with slow upgraders in the past.

https://docs.python.org/3/library/datetime.html#datetime.timezone.utc sadly doesn't list when it was added; possibly 3.2.

[cjwatson]

datetime.timezone.utc was indeed added in Python 3.2. That would require testrepository dropping support for Python 2 (which I assume only hasn't been done because nobody has got round to it yet, but can you confirm that?).

[rbtcollins]

I think its dropped in every way that matters. We can remove the classifier as well of course.

[kloczek]

Additionally zoneinfo has been introduced in python 3.9 https://docs.python.org/3/library/zoneinfo.html
Python 3.8 will be EOSed in few weeks (Oct this year).

[cjwatson]

This is true, but it's moot since there's absolutely no point in using zoneinfo for UTC. It's only needed when you need other timezones from the IANA database.

[kloczek]

Both modules ze in standard OOTB set.
If you have any idea how to measure reading UTC time over zoneinfo or datetime metrics values taken from such reads should be used to make final decision.

[cjwatson]

Even the zoneinfo docs mention using timezone.utc for the UTC case.

[cjwatson]

#64 drops Python 2 support. If that looks good then we can take advantage of py3-specific timezone handling after that.

[rbtcollins]

Sorry, I misspoke before about introduction time. I meant datetime.UTC - which was added in 3.11 -

datetime.UTC

    Alias for the UTC time zone singleton [datetime.timezone.utc](https://docs.python.org/3/library/datetime.html#datetime.timezone.utc).

    Added in version 3.11.

I've merged #64, and will happily merge a change that uses datetime.timezone.utc.