[Zope3-dev] Re: [Python-Dev] Holes in time

[Guido van Rossum]

> So, at the moment, I don't have an actual use case in hand anymore that
> requires a from_utc() method.  astimezone() could be written in terms of it,
> though:
> 
> def astimezone(self, tz):
>     self -= self.utcoffset()  # as UTC
>     other = self.replace(tzinfo=tz)
>     return other.from_utc()
> 
> and the tzinfo base class could supply a default from_utc() method capturing
> the current astimezone() implementation.  Then we'd have a powerful hook
> tzinfo subclasses could override -- but I'm not sure anyone will find a need
> to!

That's a potentially powerful idea (but call it fromutc() since
utcoffset() doesn't have an underscore either).  I'd also then perhaps
favor the idea of implementing utcoffset() in that base class as
returning a fixed standard offset plus whatever dst() returns --
though that requires us to fix the name and type of the offset, and
may require a special case for when dst() returns None, so maybe it's
not worth it.

--Guido van Rossum (home page: http://www.python.org/~guido/)