[Datetime-SIG] Another round on error-checking

[Tim Peters]

[Carl Meyer <carl at oddbird.net>]
> That's pretty much what I proposed in the first invalid-time-checking
> thread. Alex didn't like it because `utcoffset()` is called from so many
> different places:
> https://mail.python.org/pipermail/datetime-sig/2015-August/000499.html

That is a potential problem.

> AFAICT, you are re-proposing the same solution you characterized several
> times earlier as "spraying errors all over the place" and "going nowhere
> fast." :-)

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.