[Datetime-SIG] PEP 495 (Local Time Disambiguation) is ready for pronouncement

Tim Peters tim.peters at gmail.com
Tue Aug 18 20:58:24 CEST 2015

[Alexander Belopolsky <alexander.belopolsky at gmail.com>]
> ...
> Note that when it comes to timekeeping, things are very culture-dependent.
> For example, I was told that for Chinese, future is behind your back because
> you can see the past, but not the future.  Thus, while it seems natural for
> us that "first" is earlier than the "second", it may as well be the opposite
> for other people.

Then it's good that "later" doesn't suffer this hypothetical problem
;-)  In English there's no possible confusion between what "earlier"
and "later" mean when applied to time.

>  Another example that gets me confused in English usage is
> to "advance the time".  Does it mean to move to a later or to the earlier
> time?  And how does it match the "in advance" idiom?

I've always had a similar problem when people talk about a time zone
being "ahead of" or "behind" GMT (or, later, UTC).  Because different
people can and do use each term with both meanings.  Indeed, that's
why, much as it continues to irk you ;-) , the datetime docs talk
about the literally senseless (yet universally understood) "west of"
and "east of" UTC.

> I think it is actually better to use a less loaded word "fold" and explain
> that we consider the earlier of the two ambiguous times to be "regular" and
> the later to be "in the fold" than hope that users understand what "first"
> means without explanation.

Arguing that it's good to use a word nobody understands _because_
nobody understands it requires about 6 more pages of argument than
that to succeed ;-)

But, seriously, I still think it should be "_later" or "_first"
instead:  99.9973% of users will never have a need to understand what
it means.  The datetime and tzinfo implementers will make it work by
magic for them in almost all cases.  At worst, the 0.0027% of users
remaining may get irked by some anal software asking them "you know,
the time you specified is ambiguous in your current time zone - did
you intend the earlier or later time?".  They'll reboot their computer
and hope the question goes away ;-)

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