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

Carl Meyer carl at oddbird.net
Tue Aug 18 20:54:11 CEST 2015

On 08/18/2015 12:41 PM, Alexander Belopolsky wrote:
> On Tue, Aug 18, 2015 at 2:22 PM, Carl Meyer <carl at oddbird.net
> <mailto:carl at oddbird.net>> wrote:
>     But I still think I could figure out whether to use later=True or
>     later=False more easily than I could figure out whether to use fold=True
>     or fold=False (in both cases really, but especially in the gap case).
> I am not sure Raymod Hettinger is receiving these emails, so I added him
> to "bcc".  It will be good to have an input from people with teaching
> experience.  The problem with "hardcoding" the temporal relationship in
> the name of the flag is that for a missing time `t` you get a
> counter-intuitive t.replace(later=True) - t.replace(later=False) < 0. 
> On one hand, this strongly suggests that something is wrong with `t`,
> but also invites a question why not make this an error?  A "gap" is a
> negative "fold" rule may not be much better in terms of teachability,
> but it is hard to judge it without an actual teaching experience.

`t.replace(later=True) - t.replace(later=False) < 0` certainly seems
wrong, but why would it be implemented that way?

I now see that your PEP text specifies the same "backwards from the
plain sense of the flag" behavior with `first` as the flag: "The value
returned by dt.timestamp() given a missing dt will be the larger of the
two "nice to know" values if dt.first  == True and the smaller otherwise."

Why not simply flip the sense of that sentence so that `later` always
means the later of the two possible resolutions?


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