MRAB wrote:
float("nan") can occur multiple times in a set or as
a key in a dict:
>>> {float("nan"), float("nan")}
{nan, nan}
except that sometimes it can't:
>>> nan = float("nan")
>>> {nan, nan}
{nan}
NaNs are weird. They're not equal to themselves:
Python 2.7 (r27:82500, Oct 15 2010, 21:14:33)
[GCC 4.2.1 (Apple Inc. build 5664)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> nan = float("nan")
>>> nan == nan
False
This confuses the daylights out of Python's dict lookup machinery,
which assumes that two references to the same object can't possibly
compare unequal, so it doesn't bother calling __eq__ on them.
--
Greg
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