"Jim Jewett" <[EMAIL PROTECTED]> wrote: > > >> For 0: hash(+0.0)==hash(-0.0)==hash(0)=hash(0L)=0 > > > Unfortunately, that assumes that equality is transitive. > > No, but the (transitively closed set of equivalent objects) must have > the same hash. ...
Er, how do you have a transitive closure for a non-transitive operation? I really do mean that quite a lot of floating-point bells and whistles are non-transitive. The only one most people will have come across is IEEE NaNs, where 'a is b' does not imply 'a == b', but there are a lot of others (and have been since time immemorial). I don't THINK that IEEE 754R decimal introduces any, though I am not prepared to bet on it. > > let us say that I am implementing a special function and want to > > distinguish -0.0 and +0.0. Why can't I use a dictionary? > > Because they are equal. They aren't identical, but they are equal. You have missed my point, which is extended floating-points effectively downgrade the status of the purely numeric comparisons, and therefore introduce a reasonable requirement for using a tighter match. Note that I am merely commenting that this needs bearing in mind, and NOT that anything should be changed. > > >>> a = float("+0.0") > > >>> b = float("-0.0") > > >>> print a, b > > 0.0 -0.0 > > With the standard windows distribution, I get just > > 0.0 0.0 Watch that space :-) Expect it to change. Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: [EMAIL PROTECTED] Tel.: +44 1223 334761 Fax: +44 1223 334679 _______________________________________________ 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