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 ;-)