An encoder that can encode a decimal number to a string in any base, and vice versa.

base_encoder.py

class BaseEncoder:
    """ 
    An encoder that can encode a decimal number to a string in any base, and vice versa.

    Example usage:
    
        >>> import string
        >>> chars_62 = string.digits + string.ascii_letters[:52]
        >>> encoder = BaseEncoder(chars_62)
        >>> encoder.encode(10765432100123456789)
        'cPfNbbhTpel'
        >>> encoder.decode('cPfNbbhTpel')
        10765432100123456789L
    """ 
    
    def __init__(self, chars):
        self.__chars = chars
        self.__indices = {c: i for i, c in enumerate(chars)}
        self.__base_size = len(chars)

    def encode(self, n): 
        encoded = []
        while n > 0:
            n, r = divmod(n, self.__base_size)
            encoded.append(self.__chars[r])
        return ''.join(encoded[::-1])

    def decode(self, s): 
        n = 0L
        for c in s:
            n = n * self.__base_size + self.__indices[c]
        return n


if __name__ == '__main__':
    import doctest
    doctest.testmod()