[Python-Dev] Aware datetime from naive local time Was: Status on PEP-431 Timezones

[Chris Barker]

Sorry to be brain dead here, but I'm a bit lost:

On Fri, Apr 10, 2015 at 4:32 PM, Alexander Belopolsky <
alexander.belopolsky at gmail.com> wrote:

> For any given geographical location, loc, and a moment in time t expressed
> as UTC time, one can tell what time was shown on a "local clock-tower."
> This defines a function  wall(loc, t).   This function is a piece-wise
> linear function which may have regular or irregular discontinuities.
>

got it.


>   Because of these discontinuities, an equation wall(loc, t) = lt may have
> 0, 1
> or 2 solutions.
>

This is where I'm confused -- I can see how going from "wall" time ("local"
time, etc) to UTC has 0, 1, or 2 solutions:

One solution most of the time

Zero solutions when we "spring forward" -- i.e. there is no 2:30 am
on March 8, 2015 in the US timezones that use DST

Two solutions when we "fall back", i.e. there are two 2:30 am Nov 1, 2015
in the US timezones that use DST

But I can't see where there are multiple solutions the other way around --
doesn't a given UTC time map to one and only one "wall time" in a given
timezone?

Am I wrong, or is this a semantic question as to what "wall" time means?

Thanks for any clarification,

-Chris



-- 

Christopher Barker, Ph.D.
Oceanographer

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