base_26.py

def base26_encode(n, max_len=6):
    # base-26 alphabet (A-Z)
    value = ''
    digits = n
    while digits > 0:
        if len(value) == max_len:
            raise ValueError(n)
        value += chr((digits % 26) + A)
        digits /= 26
    value += 'A' * max(max_len - len(value), 0)
    return value[::-1]


def base26_decode(string):
    # base-26 alphabet
    value = 0
    for digit in string:
        digit = (ord(digit) - A)
        if digit < 0 or digit > 26:
            raise ValueError(string)
        value = value * 26 + digit
    return value