Be an AGTC programmer.

agtc.py

#!/usr/bin/env python3.6
import sys


a = 'AGTC'

def encode(s):
    out = []
    for c in s.encode():
        seq = [
            a[(c & 0xC0) >> 6],
            a[(c & 0x30) >> 4],
            a[(c & 0x0C) >> 2],
            a[(c & 0x03) >> 0]]
        out.append(''.join(seq))
    return ''.join(out)


def decode(s):
    out = []
    for c in range(0, len(s), 4):
        seq = [
            a.index(s[c+0]) << 6,
            a.index(s[c+1]) << 4,
            a.index(s[c+2]) << 2,
            a.index(s[c+3]) << 0]
        out.append(sum(seq))
    return(bytes(out).decode())


def transcript(s):
    lut = dict(zip('AGTC', 'UCAG'))
    out = ''
    for c in s:
        out += lut[c]
    return out


def main():
    plain = sys.argv[-1]
    print(f'Plain:    {plain}')
    print(f'DNA:      {encode(plain)}')
    print(f'RNA:      {transcript(encode(plain))}')
    print(f'Enc->Dec: {decode(encode(plain))}')

if __name__ == '__main__':
    main()