Mark Dickinson <dickinsm <at> gmail.com> writes: > > On Thu, Mar 25, 2010 at 12:39 PM, Jesus Cea <jcea <at> jcea.es> wrote: > > > > But IEEE 754 was created by pretty clever guys and sure they had a > > reason for define things in the way they are. Probably we are missing > > something. > > Well, if we are, then nobody seems to know what! See the Bertrand > Meyer blog post that was linked to up-thread.
The missing part, IMO, is that allowing a given NaN value to compare equal to itself only pushes the problem up one level. Any single operation yielding a NaN will still be unequal to itself. That is, under what is being proposed, with a function func() returning the same result of some calculation: x = func() s1 = (x) print x in s1 print func() in s1 This would print True and False, even though func() is perfoming the same calculation and thus logically returning the same NaN. I think the IEEE NaN represent the fact that you have a number of an undefined set, but it doesn't specify which. The only way out, IMO, is to make *all* NaN comparisons yield False, but identity yield true. No interning necessary. At most, you could make the identity function return False for the different types of NaN. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
