On Thu, Sep 18, 2014 at 2:33 AM, cool-RR <ram.rac...@gmail.com> wrote: > On Wednesday, September 17, 2014 6:30:04 PM UTC+3, Chris Angelico wrote: >> On Thu, Sep 18, 2014 at 1:16 AM, cool-RR <ram.rac...@gmail.com> wrote: >> > I didn't ask for the modulo, I agree it should remain NaN. I'm talking >> > about the floor division. >> >> Invariant: div*y + mod == x. >> If mod is NaN, there is no possible value for div that will make the >> invariant true, ergo it too has to be NaN. >> ChrisA > > Chris, why is this invariant `div*y + mod == x` so important? Maybe it's more > important to return a mathematically reasonable result for the the > floor-division result than to maintain this invariant?
It's important because it's documented :) You can expect whatever you like, but if something's a documented invariant, that's more important than your expectations. Now, why was divmod documented as returning values adhering to that invariant? You'd have to ask the developers, I've no idea. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
