On Fri, Jul 3, 2015 at 12:52 AM, Steven D'Aprano <st...@pearwood.info> wrote: > Can anyone reproduce this behaviour? If so, please reply with the version of > Python and your operating system. Printing sys.version will probably do. > > > x = 1 - 1/2**53 > assert x == 0.9999999999999999 > for i in range(1, 1000000): > if int(i*x) == i: > print(i); break >
I suspect for Py2 you need to say 1/2.0, or insist on a future directive. Otherwise the assertion fails, x is simply 1, and the loop instantly halts, none of which is buggy behaviour. Testing on a 64-bit Debian Jessie, these all run to completion: Python 3.6.0a0 (default:5c901b39c6b7, Jun 28 2015, 09:13:39) Python 3.5.0b1+ (default:7255af1a1c50+, May 26 2015, 00:39:06) Python 3.4.2 (default, Oct 8 2014, 10:45:20) Python 2.7.9 (default, Mar 1 2015, 12:57:24) Testing on a 32-bit Debian Jessie, these all print 2049 and stop: Python 3.4.2 (default, Oct 8 2014, 13:14:40) Python 3.3.3 (default, Dec 31 2013, 19:11:08) Python 2.7.9 (default, Mar 1 2015, 18:22:53) Python 2.6.6 (r266:84292, Dec 27 2010, 00:02:40) (2.6.6 isn't actually supported on Jessie, it just happens to be laying around.) On 32-bit AntiX, these both print 2049 and stop: Python 3.4.3+ (default, Jun 2 2015, 14:09:35) Python 2.7.10 (default, Jun 1 2015, 16:21:46) Looks like it's an issue with 32-bit builds only. And not on Windows - I spun up a Win 7 VM and tested it to completion: Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32 Python 2.7.10 (default, May 23 2015, 09:40:32) [MSC v.1500 32 bit (Intel)] on win32 Over-eager optimization somewhere? ChrisA -- https://mail.python.org/mailman/listinfo/python-list
