I think the algorithm is not correct.
The second step you need to sum the digits of the products instead of substract 9. Reference: Wikipedia.
In the Wikipedia you have this example:
def luhn_checksum(card_number):
def digits_of(n):
return [int(d) for d in str(n)]
digits = digits_of(card_number)
odd_digits = digits[-1::-2]
even_digits = digits[-2::-2]
checksum = 0
checksum += sum(odd_digits)
for d in even_digits:
checksum += sum(digits_of(d*2))
return checksum % 10
def is_luhn_valid(card_number):
return luhn_checksum(card_number) == 0
result = is_luhn_valid(4532015112830366)
print 'Correct:' + str(result)
result = is_luhn_valid(6011514433546201)
print 'Correct:' + str(result)
result = is_luhn_valid(6771549495586802)
print 'Correct:' + str(result)
Result:
>>>Correct:True
>>>Correct:True
>>>Correct:True