Yet another way:

a = [ 1,   9,   3,   4,   5,   6,   7,   2,   4,   3 ]
b = ['x', 'y', 'z', 'z', 'a', 'z', 'z', 'z', 'b', 'c']

anew = []
for  i, t in enumerate(zip(a, b)):
    n, c = t
    if i > 0 and c == 'z' and c == b[i-1]:
        pass
    else:
        anew.append(n)
print anew
[download]

which prints:

[1, 9, 3, 5, 6, 4, 3]
[download]

;-)