python - 这是用 Python 编写 Luhn 算法的最有效方法吗？

Question

这是我的 Luhn 算法(信用卡检查器)代码。好不好...

card = raw_input("Enter your credit card number here: ")
card = list(str(card))
card = [int(x) for x in card]
check = card[-1]
del(card[-1])
card[::2] = [2*x for x in card[::2]]
for i, x in enumerate(card):
        card[i] = sum(map(int, str(x)))
card = sum(card) * 9
card = list(str(card))
card = [int(x) for x in card]
if card[-1] == check:
    print("Card is valid!")
else:
    print("Card is invalid!")

或者我可以让它更短/更高效吗？

Answer 1

看起来您正在计算校验位的值以检查数字，但您不必这样做。校验位的要点在于，当与其余数字组合时，它会产生一个特定的结果——一个可以被 10 整除的数字。

您可以在一个循环中完成所有操作，无需中间列表，最简单的解释方法是:

card = raw_input("Enter your credit card number here: ")
digit_sum = 0

for i, digit in enumerate(reversed(card)):
    n = int(digit)

    if i % 2 == 0:
        digit_sum += n
    elif n >= 5:
        digit_sum += n * 2 - 9
    else:
        digit_sum += n * 2

if digit_sum % 10 == 0:
    print("Card is valid!")
else:
    print("Card is invalid!")