On 3/9/07, Steven Bethard <[EMAIL PROTECTED]> wrote: > On 3/9/07, Collin Winter <[EMAIL PROTECTED]> wrote: > > One solution that just occurred to me -- and that skirts the issue of > > choosing an interpretation -- is that, when comparing date and > > datetime objects, the datetime's .date() method is called and the > > result of that call is compared to the original date. That is, > > > > datetime_obj < date_obj > > > > is implicitly equivalent to > > > > datetime_obj.date() < date_obj > > Using the .date() is fine when the year/month/day doesn't match. So > the following are fine:: > datetime.datetime(2005, 1, 1, 0, 0, 0) < datetime.date(2006, 1, 1) > datetime.datetime(2007, 1, 1, 0, 0, 0) > datetime.date(2006, 1, 1) > It's *not* okay to say that a date() is less than, greater than or > equal to a datetime() if the year/month/day *does* match. The correct > temporal relation is During, but Python doesn't have a During > operator. During is not the same as less-than, greater-than or > equal-to, so all of these should be False:: > datetime.datetime(2006, 1, 1, 0, 0, 0) < datetime.date(2006, 1, 1) > datetime.datetime(2006, 1, 1, 0, 0, 0) > datetime.date(2006, 1, 1) > datetime.datetime(2006, 1, 1, 0, 0, 0) == datetime.date(2006, 1, 1) > That is, the datetime() is not less than, greater than or equal to the > corresponding date(). > > Some discussion of these kinds of issues is here: > http://citeseer.ist.psu.edu/allen94actions.html > The essence is that in order to properly compare intervals, you need > the Meets, Overlaps, Starts, During and Finishes operators in addition > to the Before (<) and Simulaneous (=) operators. > > So, let's not conflate Before, After or Simultaneous with the other > relations -- if it's not strictly Before (<), After (>) or > Simultaneous (=), we can just say so by returning False. > > (I believe these semantics would be just fine for both of the examples > offered so far, but let me know if you think that's not true.)
I can't say I'm well-versed in the intricacies of date/time issues, but what you say makes sense. This is exactly why I brought this patch up here : ) Thanks, Collin Winter _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
