'''
Credit Card check digit checker.
The Luhn Algorithm is explained here:
 https://gizmodo.com/how-credit-card-numbers-work-1493331190
'''

def weighting(digit, weight):
    n=digit*weight
    w=(n // 10 + n % 10)
    return w


evenWeight=2
oddWeight=1
t=0

cCardN=[5,4,5,7,6,2,3,8,9,8,2,3,4,1,1,3]  #This is a 16 digit credit card number
l=(len(cCardN))

for i in range (0, l-1,2):
        t=t+ weighting(cCardN[i],evenWeight)
for i in range (1, l-1,2):
        t=t+weighting(cCardN[i],oddWeight)


remainder = t % 10
calcedCD= (10 - remainder) % 10
if cCardN[l-1] == calcedCD:
    print("The calculated check digit and the last digit match!")
else:
    print("Oops! The calculated check digit doesn't match the last one read in.")