float("nan") in set or as key

[Christian Heimes]

Am 29.05.2011 19:44, schrieb MRAB:
> Would there be any advantage to making NaN a singleton? I'm thinking
> that it could make checking for it cheaper in the implementation of
> sets and dicts. Or making NaN unhashable?

It can't be a singleton, because IEEE 754 specifies millions of millions
of different NaN values. There are positive and negative NaNs, quiet
NaNs and signaling NaNs. 50 of 52 mantissa bits can vary freely, one bit
makes the difference between signaling and quiet NaNs and at least one
bit must be non-zero.

Christian