creditCardValidator.py

# python credit card validator program

# 1. Remove any '-' or ' '
# 2. Add all digits in the odd places from right to left
# 3. Double every second digit from right to left
# (If result is a two-digit number, add the two-digit number
#  together to get a single digit)
# 4. Sum the total of steps 2 & 3
# 5. If sum is divisible by 10, the credit card # is valid

sum_odd_digits = 0
sum_even_digits = 0
total = 0

# Step1
card_number = input("Enter a credit card #: ")
card_number = card_number.replace("-", "")
card_number = card_number.replace(" ", "")
card_number = card_number[::-1]

# step2
for x in card_number[::2]:
    sum_odd_digits += int(x)

# step3
for x in card_number[1::2]:
    x = int(x) * 2
    if x >= 10:
        sum_even_digits += (1 + (x % 10))  # Check the indentation of this line
    else:
        sum_even_digits += x

# step 4
total = sum_odd_digits + sum_even_digits

# step 5
if total % 10 == 0:
    print("VALID")
else:
    print("INVALID")