[Python-Dev] Negative timedelta strings

[Chris Barker]

On Fri, Mar 28, 2014 at 2:52 PM, Fred Drake <fred at fdrake.net> wrote:

> On Fri, Mar 28, 2014 at 5:19 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
> wrote:
> > ISO 8601 doesn't seem to define a representation for
> > negative durations, though, so it wouldn't solve the
> > original problem.
>
> Aside from the horribleness of the ISO 8601 notation for a duration, it's
> best not to confuse the notions of duration and delta.  Notionally, a delta
> contains more information than a duration.


and less -- really it's different.

A duration would be really useful actually, for things like "next month",
etc,. IIRC, mxDateTime has something for this, but it's NOT the same as a
timedelta.

timedelta appears to be  analogous to ISO 8601's  " time interval", which
requires


   1. Start and end, such as "2007-03-01T13:00:00Z/2008-05-11T15:30:00Z"
   2. Start and duration, such as "2007-03-01T13:00:00Z/P1Y2M10DT2H30M"
   3. Duration and end, such as "P1Y2M10DT2H30M/2008-05-11T15:30:00Z"
   4. Duration only, such as "P1Y2M10DT2H30M", with additional context
   information


http://en.wikipedia.org/wiki/ISO_8601#Time_intervals

I don't think there is or should be a any direct mapping from timedelta to
ISO duration.

-Chris

-- 

Christopher Barker, Ph.D.
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