On 2015-07-02 15:52, Steven D'Aprano wrote:
Despite the title, this is not one of the usual "Why can't Python do
maths?" "bug" reports.
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
Using Jython and IronPython, the loop runs to completion. That is the
correct behaviour, or so I am lead to believe. Using Python 2.6, 2.7 and
3.3 on Centos and Debian, it prints 2049 and breaks. That should not
happen. If you can reproduce that (for any value of i, not necessarily
2049), please reply.
See also http://bugs.python.org/issue24546 for more details.
These are all on Windows 8.1 with CPython from www.python.org.
With "x = 1 - 1.0/2**53" (needed for Python 2.x) they all passed.
2.5.4 (r254:67916, Dec 23 2008, 15:19:34) [MSC v.1400 64 bit (AMD64)]
2.5.2 (r252:60911, Feb 21 2008, 13:11:45) [MSC v.1310 32 bit (Intel)]
2.6.6 (r266:84297, Aug 24 2010, 18:13:38) [MSC v.1500 64 bit (AMD64)]
2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit (Intel)]
2.7.7 (default, Jun 1 2014, 14:21:57) [MSC v.1500 64 bit (AMD64)]
2.7.7 (default, Jun 1 2014, 14:17:13) [MSC v.1500 32 bit (Intel)]
3.1.4 (default, Jun 12 2011, 14:16:16) [MSC v.1500 64 bit (AMD64)]
3.1.4 (default, Jun 12 2011, 15:05:44) [MSC v.1500 32 bit (Intel)]
3.2.5 (default, May 15 2013, 23:07:10) [MSC v.1500 64 bit (AMD64)]
3.2.3 (default, Apr 11 2012, 07:15:24) [MSC v.1500 32 bit (Intel)]
3.3.5 (v3.3.5:62cf4e77f785, Mar 9 2014, 10:35:05) [MSC v.1600 64 bit
(AMD64)]
3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit
(Intel)]
3.4.2 (v3.4.2:ab2c023a9432, Oct 6 2014, 22:16:31) [MSC v.1600 64 bit
(AMD64)]
3.4.2 (v3.4.2:ab2c023a9432, Oct 6 2014, 22:15:05) [MSC v.1600 32 bit
(Intel)]
3.5.0b2 (v3.5.0b2:7a088af5615b, May 31 2015, 06:22:19) [MSC v.1900 64
bit (AMD64)]
3.5.0b2 (v3.5.0b2:7a088af5615b, May 31 2015, 06:08:44) [MSC v.1900 32
bit (Intel)]
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