FAQ

On Wed, Sep 9, 2015 at 12:10 PM, Tim Peters wrote:
[Alex]
Definitions: An aware datetime value t is called "regular" if t.utcoffset()
does not depend on the value of the fold attribute.
[Chris Angelico]
One point to clarify here. Is the definition of "regular" based on the
timezone alone (that is to say, a UTC datetime is regular, and an
Australia/Brisbane datetime is regular, but anything in a region with
DST is always special), or are "special" datetimes only those in the
fold period?
It applies to "an aware datetime value t". That's clear already ;-)
Everything about `t` matters. In plain English `t` is "regular" if
and only if `t` is in neither a fold nor a gap. So, e.g., all `t` in
UTC are regular. In most zones with a notion of DST, there are
exactly 2 wall-clock hours per year that are not regular (in the gap
at the start of DST, and in the fold at DST end).

Okay, that's what I thought it meant. And it's easy enough to see if
two datetimes differ only in fold. The problem I was seeing was a
difficulty in recognizing whether a single datetime is special or not,
which is answered here:


On Wed, Sep 9, 2015 at 12:02 PM, Alexander Belopolsky
wrote:
If you want to know whether t is regular you have to compare t.utcoffset()
and t.replace(fold=1-t.fold).utcoffset(). If they are the same, t is
regular. If not - t is special.

Thanks Alex!


(I can imagine pushing this to the timezone object as a primitive,
which will allow it to be optimized down to "t is regular" for
timezones that are always regular, but that's an optimization only.)


ChrisA

Search Discussions

Discussion Posts

Previous

Follow ups

Related Discussions

Discussion Navigation
viewthread | post
posts ‹ prev | 23 of 26 | next ›
Discussion Overview
groupdatetime-sig @
categoriespython
postedSep 8, '15 at 1:57a
activeSep 9, '15 at 3:44p
posts26
users4
websitepython.org

People

Translate

site design / logo © 2017 Grokbase