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Python 2.7.3 (default, Aug 1 2012, 05:14:39)
[GCC 4.6.3] on linux2
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>>> x = float('nan')
>>> id(x) == id(x)
True
>>> x == x
False
I’m interested in how nan != nan in python. And just to clarify, I know nan is supposed to behave like that by definition, I’m asking about how not about why. Where is that implemented? Is there any other object which behaves like that?
For the “where” part of your questions, look starting at line 391 in Objects/floatobject.c in the Python 2.7.3 source tree. A brief discussion is given about the behavior of NaN == NaN with the implementation following.
With respect to other cases that exhibit similar behavior, it is certainly possible. I have not done an exhaustive search of the libraries however, so I can’t give a definitive answer.