[Datetime-SIG] Another round on error-checking

[Alexander Belopolsky]

On Mon, Aug 31, 2015 at 3:20 PM, Tim Peters <tim.peters at gmail.com> wrote:

>     def __hash__(self):
>         if self._hashcode == -1:
>             tzoff = self.utcoffset()
>             if tzoff is None:
>                 self._hashcode =
> hash(self.replace(first=True)._getstate()[0])
>             else:
>                 days = _ymd2ord(self.year, self.month, self.day)
>                 seconds = self.hour * 3600 + self.minute * 60 + self.second
>                 self._hashcode = hash(timedelta(days, seconds,
> self.microsecond) - tzoff)
>         return self._hashcode
>
> So it's the case that two datetimes that compare true may have
> different hashes, when they represent the earlier and later times in a
> fold.  I didn't say "it's a puzzle" lightly ;-)
>

Yes, it looks like I have a bug there, but isn't fixing it just a matter of
moving self.replace(first=True) up two lines?  Is there a bigger puzzle?
Certainly x == y ⇒ hash(x) == hash(y) is the implication that I intend to
preserve in all cases.
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