This isn't a bug: it was a deliberate decision, just like the choice to represent `-nan` as `nan` in `float.__repr__` was a deliberate decision. NaNs don't have a meaningful sign - they have a sign *bit*, but it's best to regard that as just an extra bit of metadata (like the payload bits).

IEEE 754 explicitly refuses to interpret the sign bit of a NaN: section 1.4 of the 2019 version of the standard says: "This standard does not specify [...] Interpretation of the sign and significand fields of NaNs."

As Vedran points out, infinities are a very different beast: the difference between negative infinity and positive infinity matters.

[Raymond]

> no application should rely on seeing a particular sign for a NaN

Yep, exactly.