[Python-Dev] PEP 495 Was: PEP 498: Literal String Interpolation is ready for pronouncement

[Alexander Belopolsky]

On Fri, Sep 11, 2015 at 8:56 PM, Random832 <random832 at fastmail.com> wrote:

> Alexander Belopolsky <alexander.belopolsky at gmail.com> writes:
> > There is no "earlier" or "later". There are "lesser" and "greater"
> > which are already defined for all pairs of aware datetimes. PEP 495
> > doubles the set of possible datetimes
>
> That depends on what you mean by "possible".
>

What exactly depends on the meaning of  "possible"?  In this context
"possible" means "can appear in a Python program."



> > and they don't fit in one
> > straight line anymore. The whole point of PEP 495 is to introduce a
> > "fold" in the timeline.
>
> That doesn't make sense. Within a given timezone, any given moment of
> UTC time (which is a straight line [shut up, no leap seconds here]) maps
> to only one local time. The point of PEP 495 seems to be to eliminate
> the cases where two UTC moments map to the same aware local time.
>

Yes, but it does that at the cost of introducing the second local "01:30"
which is "later" than the first "01:40" while "obviously" (and according to
the current datetime rules)  "01:30" < "01:40".

>
> Out of curiosity, can "fold" ever be any value other than 0 or 1?
>

Thankfully, no.

>
> > Yes, but are we willing to accept that datetimes have only partial
> > order?
>
> I apparently haven't been following the discussion closely enough to
> understand how this can possibly be the case outside cases I assumed it
> already was (naive vs aware comparisons being invalid).


Local times that fall in the spring-forward gap cannot be ordered interzone
even without PEP 495.
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