Guido van Rossum wrote:
 > Hm, OK, but then passing a zero of some other type (e.g. int) should
> also return +1 as the sign. I also think the function's name should be
> changed, because I (and I assume many others) have grown up with a
> sign() function that essentially returns cmp(x, 0.0).
> 
> Perhaps it would be better to have a function math.isneg() that
> returns True for -0.0 and anything smaller and False for +0.0 and
> anything larger. It could also return the proper sign of a nan.

I'm fine with a isneg() function but I wouldn't "fix" it for NaN. It has
probably some kind of obscure meaning. The best explanation I was able
to find, is http://www.cisl.ucar.edu/docs/trap.error/errortypes.html

"Note: Since NaN is "not a number," there really isn't a "+" or "-" sign
associated with it."

Christian