def m1(a, b):
    return list(set(a) - set(b))[:100]

def m2(a, b):
    return list(set(a).difference(b))[:100]

def m3(a, b):
    return list(islice(set(a).difference(b), 100))

def m4(a, b):
    bset = set(b)
return list(islice((x for x in a if x not in bset), 100))
How to get n elements of a list not contained in another one?