pyCreditCardChecker

# Credit Card Number Check using Luhn's Algorithm

# Starting from the right end, add up the sum of the digits, but for every other digit, double it before adding.
# Where the doubled digit results in a 2-digit number, use the sum of those two digits.

# The resulting sum should be a multiple of 10

def cc_check(cnum):
    cnum1n = [int(c) for c in cnum[::-2]]
    cnum2n = [2 * int(c) for c in cnum[:-1][::-2]]
    cnum3 = [n if n < 10 else n - 9 for n in cnum2n]
    return not (sum(cnum1n) + sum(cnum3)) % 10

cc = "4417123456789113"
print(cc, cc_check(cc))
# 4417123456789113 True

cc = "4417123456789114"
print(cc, cc_check(cc))
# 4417123456789113 False