On Sat, Sep 12, 2015 at 10:25 PM, Tim Peters <tim.pet...@gmail.com> wrote:
> > I will try to create a zoneinfo wrapping prototype as well, but I will > > probably "cheat" and build it on top of pytz. > > It would be crazy not to ;-) Note that Stuart got to punt on "the > hard part": .utcoffset(), since pytz only uses fixed-offset classes. > For a prototype - and possibly forever after - I'd be inclined to > create an exhaustive list of transition times in local time, parallel > to the list of such times already there in UTC. Yes. The only complication is that you need four transition points instead of two per year in a regular DST case: (1) start of gap; (2) end of gap; (3) start of fold; and (4) end of fold. Once you know where you are with respect to those points, figuring out utcoffset(), dst() and tzname() for either value of fold is trivial. > An index into either > list then gives an index into the other, and into the list of > information about the transition (total offset, is_dst, etc). Right. It's a shame though to work from a transitions in UTC list because most of DST rules are expressed in local times and then laboriously converted into UTC. I think I should also implement the POSIX TZ spec tzinfo. This is where the advantage of the "as intended" approach will be obvious.
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