[PYTHON DB-SIG] [comp.lang.python] Date-Time requirements (esp. for databases)

[Jim Fulton]

Harri Pasanen wrote:
> 
> Jim Fulton writes:
> > W. Craig Trader wrote:
> > >
> > > > arithmetic - difference between two dates. adding dates - it should be
> > > >            possible to produce a DateTime object representing "1 week"
> > > >            and say DateTime(now) + DateTime("1 week").
> > >
> > > I think you're wrong here - there should be multiple types:  DateTime, as
> > > already discussed, and Interval, which would represent a signed quantity
> > > of a generic unit (ie: 10 minutes or 2 hours or 1 week or 5 years), or
> > > possibly a combination.  Math would look like this:
> > >
> > >         Interval + Interval => Interval
> > >         Interval - Interval => Inverval
> > >         DateTime + Interval => DateTime
> > >         DateTime - Interval => DateTime
> > >         DateTime - DateTime => Interval
> > >
> > > Since we're talking about databases, the types should try to stick fairly
> > > close to SQL, and SQL/92 already has provisions for DateTimes and
> > > Intervals.
> >
> > What is the rational for using a dedicated Interval class rather than
> > just
> > using numbers with agreed units. (See my other note?)  Is the benefit
> > worth the added class?
> 
> I'd vote for Interval class, as the convenient unit depends on the
> application domain.  I can easily imagine applications where even
> subsecond intervals are interesting, as well as those where a day is a
> small unit.

Even if the DateTime class exported unit conversion attributes?
If I want to work in, say milliseconds, I can easily do:

  spam=(date1-date2)/DateTime.lengthOfSecond * 1000

without introducing a separate Interval class.  Isn't this enough?
If not, then how would an Interval class be used to solve this problem, 
and why would it be better?

Jim

-- 
Jim Fulton         Digital Creations
jim@digicool.com   540.371.6909
## Python is my favorite language ##
##     http://www.python.org/     ##

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