Why are timezone aware and naive datetimes not distinct classes?

Nobody nobody at nowhere.com
Sat Mar 9 20:14:55 CET 2013


On Sat, 09 Mar 2013 09:01:17 +1100, Chris Angelico wrote:

> As I see it, a naive datetime simply does not have a timezone.

The distinction between aware and naive isn't whether the .tzinfo member
is None, but whether self.utcoffset() returns None (which can occur either
if self.tzinfo is None or if self.tzinfo.utcoffset(self) returns None).

IOW, an "aware" time/datetime can be converted to a UTC time/datetime, a
"naive" one can't, although it can still have a timezone which isn't
referenced to UTC.

The distinction may actually matter for times in the far future, as you
can't reliably predict how or when timezone defintions will change.
Converting a future datetime to UTC based upon the current timezone rules
is at best an estimate. For this reason, "appointments" should always be
kept in local time, so that you don't get errors if the timezone rules
(or the timezone) change between the time an appointment is made and the
time it occurs.




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