[Datetime-SIG] PEP 495 (Local Time Disambiguation) is ready for pronouncement

Alexander Belopolsky alexander.belopolsky at gmail.com
Tue Aug 18 19:09:26 CEST 2015

On Tue, Aug 18, 2015 at 12:30 PM, Tim Peters <tim.peters at gmail.com> wrote:

> [Guido]
> >> Proposal: name the flag 'fold', reverse it's sense, and be done with it
> >> (then move on to PEP 500). So fold defaults to False.
> [Alexander]
> > I like "fold".  It is short, uses the word from the problem domain
> I suppose I'm being dense, but what does fold=True mean?  Clearly it
> means "this is an ambiguous time" - but _which_ one is intended?  The
> earlier or the later?

I had the same objection when Guido first mentioned "fold" as a side remark
in his earlier comments.  I agree that unlike "first", "fold" requires some
additional knowledge to realize that fold=False means the first and
fold=True means the second of the two moments.

The diagram is the mnemonic, not a proof that fold=True means the second:

           \  |
            \ |
fold=False   \| fold=False

You can draw a reversed diagram and argue for the opposite meaning

          |  /
          | /
fold=False|/  fold=False

For some reason, however, the first diagram feels more natural.

Note that when it comes to timekeeping, things are very culture-dependent.
For example, I was told that for Chinese, future is behind your back
because you can see the past, but not the future.  Thus, while it seems
natural for us that "first" is earlier than the "second", it may as well be
the opposite for other people.  Another example that gets me confused in
English usage is to "advance the time".  Does it mean to move to a later or
to the earlier time?  And how does it match the "in advance" idiom?

I think it is actually better to use a less loaded word "fold" and explain
that we consider the earlier of the two ambiguous times to be "regular" and
the later to be "in the fold" than hope that users understand what "first"
means without explanation.
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