On Wed, Aug 26, 2015 at 12:37 PM, Alexander Belopolsky < [email protected]> wrote:
> > On Wed, Aug 26, 2015 at 3:00 PM, Guido van Rossum <[email protected]> > wrote: > >> The proposal in PEP 495 adds a 'fold' flag whose value is 0 *except* for >> local times mapped from UTC period C-D; between C and D local time is >> between R and S with fold=1. (Note that the current text of the PEP has a >> flag named 'first' whose definition is the opposite; but the plan is to >> switch to fold=0. In any case it's one bit of information and it's only >> used for times between P-Q.) > > > I have edited [1] your sketch to show the UTC mappings of two local times: > g in the gap and f in the fold: (g, fold=0) maps to G0, (g, fold=1) maps to > G1, (f, fold=0) maps to F0, and (f, fold=1) maps to F1. Note that G1 < G0 > while F1 > F0. This may look arbitrary, but it follows from a consistent > rule: fold=0 is the intersection with the line that is solid (valid) before > the transition and fold=1 is the intersection with the line that is solid > (valid) after the transition. > > [1]: https://github.com/abalkin/ltdf/blob/master/dst-visual.jpg > Cool! Which reminds me, there are some edge cases to consider. What's the local time for UTC=A? And for UTC=C? I guess the rule is to use half-open intervals on the X axis that are open on the right, so that A maps to Q and C maps to R. -- --Guido van Rossum (python.org/~guido)
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