[Zope3-dev] Re: [Python-Dev] Holes in time

[Guido van Rossum]

> I'm confused: are you saying that Guido's calendar doesn't get
> internally converted to UTC?

That's correct.  I use a Palmpilot, which has no knowledge of
timezones or DST at all.  In fact, I write down appointments in
whatever local time I will be in on a specific date, i.e. if I were to
fly to California to meet with you at 1pm on some date, I'd put that
down for 1pm on that date; on the plane I'll set the Palmpilot's clock
back three hours.

I've heard of a calendar application on Windows (Outlook?) that
records all your appointments in UTC and displays them in local time.
That means that when you are temporarily in a different timezone and
you change your computer's clock to match local time, all your
appointments are displayed in that local time -- which means that if
you want to look up an appointment next week when you're back home, it
is shown wrong!  (E.g. a 1pm appointment in Washington DC would show
up as 10am when the user is in San Francisco -- very confusing when
you're in SF talking on the phone to a potential customer on the east
coast!)

> If not, then the chart from your message starting this thread
> doesn't apply, because here you're talking about converting from
> wall clock to wall clock, which I think is a conversion that makes
> no sense -- that perhaps would be a suitable occasion for an
> exception.

You can get from wall clock + tzinfo to UTC quite easily using the
utcoffset() method of the tzinfo -- that's what it is for.  So wall
clock to wall clock conversion reduces to UTC to wall clock
conversion anyway.

> If Guido's appointment does get converted to UTC, then there's always a
> sensible (if possibly ambiguous) conversion to wall time, and if he
> looks at his calendar, he should be able to see if his appointment got
> converted to UTC correctly.

No -- why would I care about UTC or even know the UTC offset of my
wall clock time?  If I make an appointment for early next April, why
should I have to know whether DST applies or not at that particular
date?

--Guido van Rossum (home page: http://www.python.org/~guido/)