Checking for nan without using isnan

Question Q9.1.5

How can you establish whether a floating point number is nan or not without using math.isnan or numpy.isnan?

Solution Q9.1.5

We cannot compare with == since nan is not equal to itself. However, it is the only floating point number which is not equal to itself, so use != instead:

In [x]: c = 0 * 1.e1000    # 0 * inf is nan
In [x]: c != c
Out[x]: True               # c isn't equal to itself, so must be nan