[Datetime-SIG] Another round on error-checking

Alexander Belopolsky alexander.belopolsky at gmail.com
Mon Aug 31 20:58:14 CEST 2015

On Mon, Aug 31, 2015 at 2:38 PM, Carl Meyer <carl at oddbird.net> wrote:
[Tim Peters]

> > Nope.  There's nothing here about, e.g., messing with datetime
> > constructors, .replace(), .combine() ... "naive time" is left alone
> > here.  It's only timezone-specific operations targeted here, which are
> > all implemented _by_ tzinfo objects.  Not by datetime itself.
> There wasn't any of that stuff (messing with constructors, or replace,
> or combine, or naive time) in what Alex and I were discussing in the
> other thread, either. Just the idea of having `utcoffset()` raise an
> error if it hit an ambiguity.

I think the main difference between Tim's current proposal and what was
previously discussed is that all older proposals somehow required  a third
value for fold.   Note that there is a third variant suggested by Guido
off-list and discussed in the PEP:  have fold=-1 by default, ignore it
unless it is nonnegative and design whatever you want for fold=0/1 without
concerns for backward compatibility.   This effectively will give two
different datetime classes: classic and new.  Both are perfectly
consistent, but if you think interoperation between naive and aware is
confusing, try to explain how new naive instances will interoperate with
classic aware!
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