2009/4/16 Antoine Pitrou <solipsis at pitrou.net>: > Paul Moore <p.f.moore <at> gmail.com> writes: >> >> Oh, certainly! But in the absence of "intuitive", I've found in the >> past that "standardised" is often better than nothing (For >> example, I use Oracle's add_months function fairly often - it's not >> perfect, and not always intuitive, but at least it's well-defined in >> the corner cases, and fine for "normal" use). > > I think something like "date.add_months()" would be better than the proposed > monthdelta. The monthdelta proposal suggests that addition is something > well-defined and rigourous, which is not really the case here (for example, if > you add a monthdelta and then substract it again, I'm not sure you always get > back the original date). I didn't particularly get that impression, but I understand what you're saying. Personally, I don't think it matters much one way or the other. But as well as monthdelta, the proposal included monthmod. I'm not entirely happy with the name, but I like the idea - and particularly the invariant dt + monthmod(dt, dt+td)[0] + monthmod(dt, dt+td)[1] == dt + td. For me, that makes it a lot easier to reason about month increments. One thing I have certainly needed in the past is a robust way of converting a difference between two dates into "natural language" - 3 years, 2 months, 1 week and 5 days (or whatever). For that type of application, monthmod would have been invaluable. In my view, monthdelta seems a lot more natural alongside monthmod, than an add_months method would. And as monthmod is a function of two dates, it can't really be a method (OK, I know, something horrid like date1.monthdiff(date2) is possible, but honestly, I don't see that as reasonable). But this type of API design discussion does emphasise why I think the module should be a 3rd party package for a while before going into the stdlib. Paul.
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