I hate eye strains

flycode.py

import itertools


def encode(s: str, encoding: str = 'utf-8', ntet: int = 8, flip: int = 0) -> str:
    if ntet < flip:
        raise ValueError('ntet must be less than flip.')

    if ntet == 8 and flip == 0:
        header = ''
    elif ntet != 8 and flip == 0:
        header = f'{ntet}_'
    else:
        header = f'{ntet}~{flip}_'

    result = [header]

    b = s.encode(encoding)
    ntet_mask = (1 << ntet) - 1
    flip_mask = 1 << (flip - 1) if flip > 0 else 0
    ntet_fmt = f'{{num:0{ntet}b}}'

    for i, octet in enumerate(b):
        num_masked = octet & ntet_mask
        if num_masked != octet:
            raise ValueError(f'Encoding failed at position {i}: Cannot represent character as a {ntet}-tet')
        encoded = ntet_fmt.format(num=num_masked ^ flip_mask)
        result.append(encoded)

    return ''.join(result)


def decode(s: str, encoding: str = 'utf-8') -> str:
    if '_' in s:
        header, s = s.split('_')
        if '~' in header:
            ntet, flip = map(int, header.split('~'))
        else:
            ntet = int(header)
            flip = 0
    else:
        ntet = 8
        flip = 0

    result = bytearray()
    for bits in itertools.batched(s, ntet):
        value = int(''.join(bits), 2)
        if flip > 0:
            value ^= 1 << (flip - 1)
        result.append(value)
    return result.decode(encoding)


if __name__ == '__main__':
    print(decode('7~4_1011100110000011011010101000110111011001001110001010100011110101111101110011011110110101000110100111111000101000110010111000011101100110011011000011101111110000011111000100110'))
    print(encode('I love cookies!', flip=1))