The sign of a NaN *is* fully supported, and easily accessible to those who need it. It just isn't part of the repr. Given that the sign is meaningless in the vast majority of applications, I think Python does the right thing here by leaving it out of the repr, rather than cluttering up the repr with meaningless and potentially confusing information.

I'll leave the last word to Stephen Canon, from the SO answer I linked to above:

" it is almost always a bug to attach meaning to the "sign bit" of a NaN datum."