def base36encode(number, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
    """Converts an integer to a base36 string."""
    if not isinstance(number, int):
        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
