Encode with custom alphabet

encoder.py

def encode_int(number: int, *, alphabet: bytes) -> bytes:
    """Encode given number using the characters from the alphabet."""
    if number < 0:
        raise ValueError('number must be positive')

    if len(alphabet) != len(set(alphabet)):
        raise ValueError('characters in the alphabet must be unique')

    if number == 0:
        return alphabet[0:1]

    encoded = []
    while number > 0:
        number, idx = divmod(number, len(alphabet))
        encoded.append(alphabet[idx])
    encoded.reverse()

    return bytes(encoded)


def encode(value: bytes, *, alphabet: bytes) -> bytes:
    """Encode given value using the characters from the alphabet."""
    number = int.from_bytes(value, 'big', signed=False)

    return encode_int(number, alphabet=alphabet)