Laura Creighton wrote: > In a message of Fri, 03 Jul 2015 00:52:55 +1000, "Steven D'Aprano" writes: >>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. >> >> >> >>-- >>Steven > > PyPy says: > Python 2.7.9 (2.5.1+dfsg-1, Mar 27 2015, 19:45:43) > [PyPy 2.5.1 with GCC 4.9.2] on linux2 > Type "help", "copyright", "credits" or "license" for more information. >>>>> x = 1 - 1/2**53 >>>>> assert x == 0.9999999999999999 > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > AssertionError >>>>> for i in range(1, 1000000): > .... if int(i*x) == i: > .... print(i); break > .... > .... > 1 >>>>> > > So the loop terminates, but there is an Assertion Error. Did you want > that?
No. Steven's environment implies from __future__ import division which he forgot to mention in the original post: >>>> x = 1-1/2**53 >>>> x 1 >>>> from __future__ import division >>>> x = 1-1/2**53 >>>> x 0.9999999999999999 -- https://mail.python.org/mailman/listinfo/python-list
