How to use numpy with ‘None’ value in Python?

You are looking for masked arrays. Here’s an example.

import numpy.ma as ma
a = ma.array([1, 2, None], mask = [0, 0, 1])
print "average =", ma.average(a)

From the numpy docs linked above, “The numpy.ma module provides a nearly work-alike replacement for numpy that supports data arrays with masks.”