Tim Chase wrote: >> Month arithmetic is a bit of a mess, since it's not clear how >> to map e.g. Jan 31 + one month. > > "Jan 31 + one month" usually means "add one to the month value and then > keep backing off the day if you get an exception making the date", so > you'd get Feb 31, exception, Feb 30, exception, Feb 29, possibly an > exception, and possibly/finally Feb 28th. This makes pretty intuitive > sense to most folks and is usually what's meant.
Well, yes, but that's just one way to solve the problem. I guess I'll just add all possible solutions and then let the user decide what's best in some way. > I've found that issues and confusion stem more from the non-commutative > reality that "Jan 31 + (1 month) + (-1 month) != Jan 31 + (-1 month) + > (1 month)" or the non-associative "Jan 31 + (1 month + 1 month) != (Jan > 31 + 1 month) + 1 month" :-/ That's why mxDateTime actually returning a day in March... >>> mx.DateTime.DateTime(2009, 1, 31) + mx.DateTime.RelativeDateTime(months=+1) <mx.DateTime.DateTime object for '2009-03-03 00:00:00.00' at 2ba43f93ebe0> That's intuitive for mathematicians only, though ;-) > So yes, messy it is! Indeed. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Oct 12 2009) >>> Python/Zope Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::: Try our new mxODBC.Connect Python Database Interface for free ! :::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
