Vedran Čačić <ved...@gmail.com> added the comment:

inf and -inf are really two different values (in the scope of the standard). 
Same as 5. and -5., or even 0. and -0. They behave differently in some exactly 
specified operations, and it is useful.

Are there any exactly specified operations whose specifications require the 
unequal treatment of nans with + and - signs? I don't think so, since it goes 
against the whole idea of nan as an unspecified number. (If you want to track 
its _history_, that's what payload is for.) My interpretation is that nan can 
have a sign bit only so unary minus and absolute value can be implemented 
quicker (without having to check whether the input is nan) -- not because it 
carries any useful semantics within the standard.

----------
nosy: +veky

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<https://bugs.python.org/issue42210>
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