Credit中的NameError-pset6 CS50x

Question

我是Python新手。我在Python中唯一的背景是CS50（第6周）。我正在尝试从pset6实现Credit。在这种情况下，我们必须实现Luhn算法。

但是，我收到了下面提到的错误，但我不明白为什么：

Traceback (most recent call last):
  File "credit.py", line 57, in <module>
    main()
  File "credit.py", line 9, in main
    if IfAmex(arr_number):
  File "credit.py", line 27, in IfAmex
    if Luhn(card_n):
  File "credit.py", line 50, in Luhn
    sum2 = sum(int(c) for c in str(2 * card_n[i]) for i in range(1, len(card_n), 2))
NameError: name 'i' is not defined

这是我的代码：

from sys import exit
from cs50 import get_int

def main():
    number = get_int("Number: ")
    # Converting the number into a list
    arr_number = [int(x) for x in str(number)]

    if IfAmex(arr_number):
        print("AMEX")
        exit(0)
    elif IfMasCard(arr_number):
        print("MASTERCARD")
        exit(0)
    elif IfVisa(arr_number):
        print("VISA")
        exit(0)
    else:
        print("INVALID")
        exit(0)

def IfAmex(card_n):
    if not len(card_n) == 15:
        return False
    if not (card_n[0] * 10 + card_n[1]) in [34, 37]:
        return False
    if Luhn(card_n):
        return True

def IfMasCas(card_n):
    if not len(card_n) == 16:
        return False
    if not (card_n[0] * 10 + card_n[1]) in range(51, 56):
        return False
    if Luhn(card_n):
        return True

def IfVisa(card_n):
    if not len(card_n) in [13, 16]:
        return False
    if not card_n[0] == 4:
        return False
    if Luhn(card_n):
        return True

def Luhn(card_n):
    # Reversing the digits
    card_n = card_n[::-1] 

    sum1 = sum(card_n[::2])
    sum2 = sum(int(c) for c in str(2 * card_n[i]) for i in range(1, len(card_n), 2)) # The Error Line

    luhnsum = sum1 + sum2

    return luhnsum % 10 == 0

if __name__ == '__main__':
    main()

我使用的测试用例是（以及正确的输出）：

$ python credit.py
Number: 378282246310005
AMEX

另外，请告诉我我是否正确使用exit()。

Answer 1

您在此处使用i作为card_n数组的索引。但是您忘了定义它。

使用前，先定义并分配一个值。

sum2 = sum(int(c) for c in str(2 * card_n[i])