[Python-Dev] Python's C interface for types (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Thu Feb 1 19:35:58 CET 2007

Nick Maclaren schrieb:

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.

If so, they just shouldn't use the equal operator (==). == ought to be transitive. It should be consistent with has().

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.

If introducing extended floating-points would cause trouble to existing operations, I think extended floating-points should not be introduced to Python. If all three of you really need them, come up with method names to express "almost equal" or "equal only after sunset".

Regards, Martin

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