[Datetime-SIG] Are there any "correct" implementations of tzinfo?
alexander.belopolsky at gmail.com
Sat Sep 12 21:53:38 CEST 2015
On Sat, Sep 12, 2015 at 3:41 PM, Tim Peters <tim.peters at gmail.com> wrote:
> > If there are not, maybe the intended semantics should go
> > by the wayside and be replaced by what pytz does.
> Changing anything about default arithmetic behavior is not a
> possibility. This has been beaten to death multiple times on this
> mailing list already, and I'm not volunteering for another round of it
Tim and Guido only grudgingly accept it, but datetime already gives you
"the pytz way" and PEP 495 makes a small improvement to it. The
localize/normalize functionality is provided by the .astimezone() method
which when called without arguments will attach an appropriate fixed offset
timezone to a datetime object. You can then add timedeltas to the result
and stay within a "fictitious" fixed offset timezone that extends
indefinitely in both directions. To get back to the actual civil time -
you call .astimezone() again. This gives you what we call here a
"timeline" arithmetic and occasionally it is preferable to doing arithmetic
in UTC. (Effectively you do arithmetic in local standard time instead of
UTC.) Using a fixed offset timezone other than UTC for timeline
arithmetic is preferable in timezones that are far enough from UTC that
business hours straddle UTC midnight.
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