To determine NaN

Math.isnan() determines whether float is NaN or not.

import math
x=float('nan')
math.isnan(x)

It checks whether float is NaN or not as same as math.isnan().

import numpy
x=float('nan')
numpy.isnan(x)

According to IEEE standard, NaN value is always false when comparing NaN value. Use this to define a function.

def isNaN(num):
    return num != num
x=float('nan')
isNaN(x)