Computing/verifying licence plates http://en.wikipedia.org/wiki/Vehicle_registration_plates_of_Singapore#Checksum

gistfile1.py

'''A-1'''
alpha2num = lambda s: (ord(char) - ord('A') + 1 for char in s)

'''0-0'''
num2num = lambda s: (ord(num) - ord('0') for num in s)

import itertools
import re

LOOKUP = ('A', 'Z', 'Y', 'X', 'U', 'T', 'S', 'R', 'P', 'M', 'L', 'K', 'J', 'H', 'G', 'E', 'D', 'C', 'B')
ZIP = (9, 4, 5, 4, 3, 2)
BASE = 19

pat = re.compile(r'([A-Z]+)([0-9]+)([A-Z]?)')

def run(plate):
    m = re.match(pat, plate)
    if not m:
        return
    prefix, body, p_letter = m.groups()
    it = itertools.chain(alpha2num(prefix[-2:]), num2num(body))
    it = zip(ZIP, it) # ZIP first ensures result is bounded by length of 1st arg instead of 2nd
    x = reduce(lambda s,(a,b): s+a*b, it, 0) # hmm destructuring works in arguments...
    letter = LOOKUP[x % BASE]
    # two modes - 1) verify, or 2) compute
    if p_letter == '':
        return letter
    else:
        return p_letter == letter