[Python-ideas] [Python-Dev] datetime module enhancements (original) (raw)

Collin Winter collinw at gmail.com
Mon Mar 12 05:59:53 CET 2007

[Moving to python-ideas...]

On 3/9/07, Steven Bethard <steven.bethard at gmail.com> wrote on python-dev:

On 3/9/07, Collin Winter <collinw at gmail.com> wrote on python-dev: > 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, > > datetimeobj < dateobj_ _> > is implicitly equivalent to > > datetimeobj.date() < dateobj

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.

It might be neat to add a contains method to date() objects so that "datetime(2007, 1, 1, 0, 0, 0) in date(2007, 1, 1)" would be True. This would seem to fulfill the During operator.

Collin Winter

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