[Python-Dev] Caching float(0.0) (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Tue Oct 3 19:27:05 CEST 2006

Nicko van Someren schrieb:

It's only a semantic change on platforms that "happen to" use IEEE 754 float representations, or some other representation that exposes the sign of zero.

Right. Later, you admit that this is vast majority of modern machines.

It would be instructive to understand how much, if any, python code would break if we lost -0.0. I'm do not believe that there is any reliable way for python code to tell the difference between all of the different types of IEEE 754 zeros and in the special case of -0.0 the best test I can come up with is repr(n)[0]=='-'. Is there an compelling case, to do with compatibility or otherwise, for exposing the sign of a zero? It seems like a numerical anomaly to me.

I think it is reasonable to admit that a) this change is a change in semantics for the majority of the machines b) it is likely that this change won't affect a significant number of applications (I'm pretty sure someone will notice, though; someone always notices).

Regards, Martin

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