python nan != nan

Question

Python 2.7.3 (default, Aug  1 2012, 05:14:39) 
[GCC 4.6.3] on linux2
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>>> x =          


        

Answer 1

Not A Number (NaN) is unequal with anything. To detect it, use math.isnan. And an object like this is quite easy to define:

class A(object):
    def __eq__(self, other):
        return False

    def __ne__(self, other):
        return True

The reason why this is is quite simple. CPython follows the IEEE 754 standard for floating point math. NaN is a floating point value for which IEEE 754 dictates that it is not equal to any other floating point value.