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

[MRAB]

On 2015-09-12 02:23, Alexander Belopolsky wrote:
>
> On Fri, Sep 11, 2015 at 8:56 PM, Random832 <random832 at fastmail.com
> <mailto:random832 at fastmail.com>> wrote:
>
>     Alexander Belopolsky <alexander.belopolsky at gmail.com
>     <mailto: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.
>
[snip]
What would happen if it's decided to stay on DST and then, later on, to
reintroduce DST?

Or what would happen in the case of "British Double Summer Time" (go
forward twice in the spring and backward twice in the autumn)?

https://en.wikipedia.org/wiki/British_Summer_Time