On Wed, 08 Dec 2010 13:01:28 -0800, John Nagle wrote: > On 12/7/2010 3:59 PM, Mark Wooding wrote: >>> Exactly one of >>> > >>> > a> b >>> > a = b >>> > a< b >>> > >>> > is true, or an type exception must be raised. >> This will get the numerical people screaming. Non-signalling NaNs are >> useful, and they don't obey these axioms. > > As a sometime numerical person, I've been screaming at this from > the other side. The problem with comparing non-signalling NaNs is that > eventually, the program has to make a control flow decision, and it may > not make it correctly.
Then use signalling NANs. Nobody is suggesting that quiet NANs should be compulsory, or are the solution for all problems. But they're a solution for some problems, which is why people use them. [...] > I personally think that comparing NaN with numbers or other > NaNs should raise an exception. There's no valid result for such > comparisons. If NAN and 1 are unordered, then NAN is not less or equal to 1, nor is it larger than 1. Hence both NAN <= 1 and NAN >= 1 are false. The problem only comes when the caller mistakenly thinks that floats are real numbers, and tries to reason about floats like they would reason about real numbers. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
