def luhn(n): r = [int(ch) for ch in str(n)][::-1] return (sum(r[0::2]) + sum(sum(divmod(d*2,10)) for d in r[1::2])) % 10 == 0
def luhn(n): r = [int(ch) for ch in str(n)][::-1] return (sum(r[0::2]) + sum(sum(divmod(d*2,10)) for d in r[1::2])) % 10 == 0