[Datetime-SIG] Are there any "correct" implementations of tzinfo?

Alexander Belopolsky alexander.belopolsky at gmail.com
Sat Sep 12 23:24:37 CEST 2015

On Sat, Sep 12, 2015 at 4:10 PM, Tim Peters <tim.peters at gmail.com> wrote:

> "A potential problem" with .astimezone()'s default is that it _does_
> create a fixed-offset zone.  It's not at all obvious that it should do
> so.  First time I saw it, my initial _expectation_ was that it
> "obviously" created a hybrid tzinfo reflecting the system zone's
> actual daylight rules, as various "tzlocal" implementations outside of
> Python do.

The clue should have been that  .astimezone() is an instance method and you
don't need to know time to create a hybrid tzinfo.  If a Local tzinfo was
available, it could just be passed to the .astimezone() method as an
argument.  You would not need .astimezone() to both create a tzinfo and
convert the datetime instance to it.

Still, I agree that this was a hack and a very similar hack to the one
implemented by pytz.   Hopefully once PEP 495 is implemented we will
shortly see "as intended" tzinfos to become more popular.
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