import numpy as np

a = np.array([[1,1,1],
              [2,2,2],
              [3,3,3]])

mask = [[1,0,0],
        [1,1,1],
        [0,1,1]]

b = np.array([1,2,3])

ma = np.ma.MaskedArray(a,mask).filled(0)

print(ma)
print(b)
print(np.dot(ma,b))
print(np.dot(a,b))