anlgorithm for credit card validation

cc_validation.py

import re


def is_credit_card_valid(n):
    credit_card_str = str(n)
    credit_card_as_list = map(int, credit_card_str)

    if not re.match('^\d{1,16}$', credit_card_str):
        return False

    double_pos = 0 if len(credit_card_str) % 2 == 0 else 1
    for pos in xrange(double_pos, len(credit_card_as_list), 2):
        value = credit_card_as_list[pos] * 2
        
        if value > 9:
            value = sum(map(int, str(value)))

        credit_card_as_list[pos] = value

    return bool(sum(credit_card_as_list) % 10 == 0)