[Python-Dev] PEP 495 accepted

[Alexander Belopolsky]

On Tue, Sep 22, 2015 at 3:01 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> ... for times that
> don't exist, "dt.astimezone(utc).astimezone(dt.tzinfo)" will normalise
> them to be a time that actually exists in the original time zone, and
> that normalisation also effectively happens when calling
> "dt.timestamp()".
>

Yes.  In fact, if you consider the canonical bijection between timestamps
and datetimes (t = EPOCH + s * timedelta(0, 1); s = (t - EPOCH) /
timedelta(0, 1)), t.astimezone(utc) and t.timestamp() become the same up to
some annoying numerical details.  The same logic applies to
u.astimezone(tzinfo) and datetime.fromtimestamp(s).  Note that I
deliberately did not mark the units on the sketches: you can think of the
UTC axis to be labeled by datetimes or by numeric timestamps.

Note that dt != dt.astimezone(utc).astimezone(dt.tzinfo) is one way to
detect that dt is in a gap, but I recommend
(dt.replace(fold=0).utcoffset() > dt.replace(fold=1).utcoffset().)
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