On 2017-09-22 14:03, alister via Python-list wrote: > On Fri, 22 Sep 2017 21:15:54 +1000, Steve D'Aprano wrote: >> On Fri, 22 Sep 2017 08:50 pm, alister wrote: >>> [snip] >>> >>> In a code review I would want the condition changed to be less noisy/ >>> confusing to the reader. >>> >>> if thing <=0: whatever >> >> Fair point, assuming they are the same. >> >> Actually, even for floats they're not the same. >> > [snip] > > I would also say that if your examples did indeed return different > results then pythons logic model has a bug.
No, it doesn't (in Python 3). NaN is not a number. It is neither larger nor smaller than zero. This behavior is correct: Python 3.6.0 |Continuum Analytics, Inc.| (default, Dec 23 2016, 12:22:00) [GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux Type "help", "copyright", "credits" or "license" for more information. >>> from math import nan >>> nan < 0 False >>> nan > 0 False >>> nan == 0 False >>> not (nan > 0) True Python 2.7 is a bit more fickle: Python 2.7.5 (default, Aug 2 2017, 11:05:32) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> from numpy import nan >>> nan < 0 False >>> nan > 0 False >>> nan == 0 False >>> not(nan > 0) True >>> cmp(nan, 0) -1 >>> cmp(0, nan) 1 Of course I see why the behavior of NaN is hard to swallow: in a sense the logical thing to do would be to raise a ValueError (or TypeError) when comparing to NaN - seeing as the operation doesn't make much sense in the first place - but it's better to not have an edge case where comparing two floats can raise, but only under very unusual circumstances. Cheers, Thomas -- Thomas Jollans -- https://mail.python.org/mailman/listinfo/python-list
