Use ZoneInfo instead of pytz on Python 3.9+

And update deps to pytz; python_version < "3.9"

• https://www.python.org/dev/peps/pep-0615/
• https://docs.python.org/dev/library/zoneinfo.html

cc @regebro 😄

[agronholm]

@regebro If you’re interested, I’d like to see some similar functionality to this added to the zoneinfo module in Python 3.10. I was going to write it myself, but I’d be happy to have an expert collaborator smile.

I’m not sure we want this in the standard library since this library has quite a few kludges to get the time zone information out of the (sometimes uncooperative) operating systems.

I am however eager to see a pytz-free version of this library. Maybe somebody should fork it if @regebro does not want to mess with zoneinfo in this one.

[pganssle]

I assume that this will be a breaking change, because pytz zones are used very differently from standard tzinfos. End users will need to stop using .localize.

@regebro If you’re interested, I’d like to see some similar functionality to this added to the zoneinfo module in Python 3.10. I was going to write it myself, but I’d be happy to have an expert collaborator 😄.