Python convert (encode/decode) base 36

base36.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# http://stackoverflow.com/a/1181922

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 = ''
    sign = ''

    if number < 0:
        sign = '-'
        number = -number

    if 0 <= number < len(alphabet):
        return sign + alphabet[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)
print base36decode('AQF8AA0006EH')

The encoding function allows the user to specify an alphabet, while the decoding function does not, therefore the decoding function is not a true inverse of the encoding function as it relies on the default alphabet.

any idea how this code could be modified to work with floats aswell?