Encodes and decodes integers as short, easy to type tokens, using custom alphabet.

intok.py

class Intok(object):
	"""Encodes and decodes integers as short, easy to type tokens, using custom
	alphabet.

	The default alphabet consists of 29 digits and uppercase letters. It has
	no vowels to eliminate accidental formation of words, and no glyphs that
	could be confused (0 and O, I and 1).
	"""
	alphabet = 'BCDFGHJKLMNPQRSTVWXZ23456789'
	case_sensitive = False

	def __init__(self, alphabet=None):
		self.alphabet = alphabet or self.alphabet

	def encode(self, number):
		if number > 0:
			sign = ''
		elif number == 0:
			sign = self.alphabet[0]
		else:
			sign = '-'
			number *= -1
		digits = []
		while number > 0:
			number, remainder = divmod(number, len(self.alphabet))
			digits.append(self.alphabet[remainder])
		return sign + ''.join(reversed(digits))

	def decode(self, token):
		if not self.case_sensitive:
			token = token.upper()
		number = 0
		sign = 1
		if token[0] == '-':
			sign = -1
			token = token[1:]
		mul = 1
		for c in reversed(list(token)):
			number += self.alphabet.upper().index(c) * mul
			mul *= len(self.alphabet)
		return sign * number

if __name__ == '__main__':
	ncdr = Intok()
	print("alphabet size: %d" % len(ncdr.alphabet))
	for i in range(200):
		e = ncdr.encode(i)
		dn = ncdr.decode(e)
		dl = ncdr.decode(e.lower())
		du = ncdr.decode(e.upper())
		assert i == dn == dl == du
		print("%7d: %4s" % (i,e))