On Sun, 2011-05-29 at 00:41 +0100, MRAB wrote:
> Here's a curiosity. float("nan") can occur multiple times in a set or as
> a key in a dict:
>
> >>> {float("nan"), float("nan")}
> {nan, nan}
>
These two nans are not equal (they are two different nans)
> except that sometimes it can't:
>
> >>> nan = float("nan")
> >>> {nan, nan}
> {nan}
This is the same nan, so it is equal to itself.
Two "nan"s are not equal in the manner that 1.0 and 1.0 are equal:
>>> 1.0 == 1.0
True
>>> float("nan") == float("nan")
False
I can't cite this in a spec, but it makes sense (to me) that two things
which are nan are not necessarily the same nan.
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