base 36を使用します。以下は、ウィキペディアで見つけることができる Python 実装の適応バージョンです。
def base36encode(number, alphabet='0123456789abcdefghijklmnopqrstuvwxyz'):
"""Converts an integer to a base36 string."""
if not isinstance(number, (int, long)):
raise TypeError('number must be an integer')
base36 = '' if number != 0 else '0'
sign = ''
if number < 0:
sign = '-'
number = -number
while number != 0:
number, i = divmod(number, len(alphabet))
base36 = alphabet[i] + base36
return sign + base36
def base36decode(number):
return int(number, 36)
>>> print base36encode(1412823931503067241)
aqf8aa0006eh
>>> print base36decode('aqf8aa0006eh')
1412823931503067241