In article <mailman.2395.1369891346.3114.python-l...@python.org>, Chris Angelico <ros...@gmail.com> wrote:
> On Thu, May 30, 2013 at 3:10 PM, Steven D'Aprano > <steve+comp.lang.pyt...@pearwood.info> wrote: > > # Wrong, don't do this! > > x = 0.1 > > while x != 17.3: > > print(x) > > x += 0.1 > > > > Actually, I wouldn't do that with integers either. There are too many > ways that a subsequent edit could get it wrong and go infinite, so I'd > *always* use an inequality for that: > > x = 1 > while x < 173: > print(x) > x += 1 There's a big difference between these two. In the first case, using less-than instead of testing for equality, you are protecting against known and expected floating point behavior. In the second case, you're protecting against some vague, unknown, speculative future programming botch. So, what *is* the right behavior if somebody were to accidentally drop three zeros into the source code: > x = 1000 > while x < 173: > print(x) > x += 1 should the loop just quietly not execute (which is what it will do here)? Will that make your program correct again, or will it simply turn this into a difficult to find bug? If you're really worried about that, why not: > x = 1 > while x != 173: > assert < 172 > print(x) > x += 1 -- http://mail.python.org/mailman/listinfo/python-list
