On Nov 9, 11:37 am, Steven D'Aprano <steve +comp.lang.pyt...@pearwood.info> wrote: > On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote: > > On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence <breamore...@yahoo.co.uk> > > wrote: > >> On 07/11/2012 01:55, Steven D'Aprano wrote: > > >>> Who knows? Who cares? Nobody does: > > >>> n -= n > > >> But I've seen this scattered through code: > > >> x := x - x - x > > > Can you enlighten us as to how this is better than either: > > x := -x > > or > > x := 0 - x > > ? I'm not seeing it. > > I'm hoping that Mark intended it as an example of crappy code he has > spotted in some other language rather than a counter-example of something > you would do. > > To be pedantic... there may very well be some (rare) cases where you > actually do want x -= x rather than just x = 0. Consider the case where x > could be an INF or NAN. Then x -= x should give x = NAN rather than zero. > That may be desirable in some cases.
In x86 assembler mov ax, 0 is 4 bytes sub ax, ax is 2 and therefore better (at least for those brought up on Peter Norton); the most common being xor ax, ax -- http://mail.python.org/mailman/listinfo/python-list
