replace zeroes in numpy array with the median value

This solution takes advantage of numpy.median:

import numpy as np
foo_array = [38,26,14,55,31,0,15,8,0,0,0,18,40,27,3,19,0,49,29,21,5,38,29,17,16]
foo = np.array(foo_array)
# Compute the median of the non-zero elements
m = np.median(foo[foo > 0])
# Assign the median to the zero elements 
foo[foo == 0] = m

Just a note of caution, the median for your array (with no zeroes) is 23.5 but as written this sticks in 23.