Verhoeff Checksum

gistfile1.py

# http://en.wikibooks.org/wiki/Algorithm_Implementation/Checksums/Verhoeff_Algorithm#Python

verhoeff_table_d = (
    (0,1,2,3,4,5,6,7,8,9),
    (1,2,3,4,0,6,7,8,9,5),
    (2,3,4,0,1,7,8,9,5,6),
    (3,4,0,1,2,8,9,5,6,7),
    (4,0,1,2,3,9,5,6,7,8),
    (5,9,8,7,6,0,4,3,2,1),
    (6,5,9,8,7,1,0,4,3,2),
    (7,6,5,9,8,2,1,0,4,3),
    (8,7,6,5,9,3,2,1,0,4),
    (9,8,7,6,5,4,3,2,1,0))

verhoeff_table_p = (
    (0,1,2,3,4,5,6,7,8,9),
    (1,5,7,6,2,8,3,0,9,4),
    (5,8,0,3,7,9,6,1,4,2),
    (8,9,1,6,0,4,3,5,2,7),
    (9,4,5,3,1,2,6,8,7,0),
    (4,2,8,6,5,7,3,9,0,1),
    (2,7,9,3,8,0,6,4,1,5),
    (7,0,4,6,9,1,3,2,5,8))

verhoeff_table_inv = (0,4,3,2,1,5,6,7,8,9)

def calcsum(number):
    """For a given number returns a Verhoeff checksum digit"""
    c = 0
    for i, item in enumerate(reversed(str(number))):
        c = verhoeff_table_d[c][verhoeff_table_p[(i+1)%8][int(item)]]
    return verhoeff_table_inv[c]

def checksum(number):
    """For a given number generates a Verhoeff digit and
    returns number + digit"""
    c = 0
    for i, item in enumerate(reversed(str(number))):
        c = verhoeff_table_d[c][verhoeff_table_p[i % 8][int(item)]]
    return c

def generateVerhoeff(number):
    """For a given number returns number + Verhoeff checksum digit"""
    return "%s%s" % (number, calcsum(number))

def validateVerhoeff(number):
    """Validate Verhoeff checksummed number (checksum is last digit)"""
    return checksum(number) == 0

# Some tests and also usage examples
assert calcsum('75872') == 2
assert checksum('758722') == 0
assert calcsum('12345') == 1
assert checksum('123451') == 0
assert calcsum('142857') == 0
assert checksum('1428570') == 0
assert calcsum('123456789012') == 0
assert checksum('1234567890120') == 0
assert calcsum('8473643095483728456789') == 2
assert checksum('84736430954837284567892') == 0
assert generateVerhoeff('12345') == '123451'
assert validateVerhoeff('123451') == True
assert validateVerhoeff('122451') == False
assert validateVerhoeff('128451') == False