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

Jon Ribbens jon+python-dev at unequivocal.co.uk
Sat Mar 10 13:05:38 CET 2007

Steven Bethard <steven.bethard at gmail.com> wrote:

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.

Why not? That only makes sense if you decide that a Python 'date' means 'the entire of that day'. It's not at all clear that that's what a Python 'date' does mean. And, as I mentioned before, if you do decide that then what Python currently does when you subtract dates is broken.

I just found another case where 'date's pretend to have a time-part of midnight - if you add a date to a timedelta. Add 23 hours to a date and it's unchanged - add 24 and it moves forward a day. If a 'date' really is 'the entire of that day', then adding a timedelta to it which is not an integer multiple of 1 day should either raise an exception, or return some 'time duration' object that doesn't currently exist.

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::

I think you're assuming the Python datetime module has higher goals than it does. It doesn't have any concept of a duration in time, not unless you couple a 'datetime' with a 'timedelta' yourself. And 'timedelta's are restricted to periods of time that are a fixed number of seconds - i.e. there is no way to indicate "a month" or "a year" (although that lack is a whole different argument ;-) )

Your argument is quite correct if you're considering some fancy uber-complicated kitchen-sink-included all-encompassing "temporal logic package", but that's not what Python's datetime is, nor frankly is what it should be.

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