Calcular digito verificador do ISBN

isbn.py

import unittest

def ISBN(isbn):
    """
    Autor: fzmaster
    Data: 29/12/2010
    Problema: Books for Mars
              http://codingkata.org/katas/unit/mars-books
    Calcular digito verificador do ISBN
    """
    return (10-(3*(int(isbn[1]) + int(isbn[3]) + int(isbn[5]) + int(isbn[7]) + int(isbn[9]) + int(isbn[11])) + int(isbn[0]) + int(isbn[2]) + int(isbn[4]) + int(isbn[6]) + int(isbn[8]) + int(isbn[10])) % 10) % 10 

class ISBNTestCase(unittest.TestCase):

    def test_caso1(self):
        assert ISBN('978030640615') == 7
    def test_caso2(self):
        assert ISBN('978857780013') == 1
    def test_caso3(self):
        assert ISBN('978857522247') == 8
    def test_caso4(self):
        assert ISBN('978857522212') == 6

if __name__ == '__main__':
    unittest.main()