len([x for x in list1 if x in list2])
# using numpy import numpy as np a = np.array([1,2,3,2,3,4,3,4,5,6]) b = np.array([7,2,10,2,7,4,9,4,9,8]) # using intersect1d print(np.intersect1d(a,b)) # output # [2 4]