ヴィジュネル暗号(Vigenère cipher)

vigenere_cipher.py

from itertools import cycle
a = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
chrs = cycle('ZABCDEFGHIJKLMNOPQRSTUVWXY')
table = {l: {a[i-1]: c for c, i in zip(chrs, range(26)) if i != 0} for l in a}

def encode(message: str, key: str) -> str:
  return ''.join(
    c if u else c.lower() for c, u in (
      (table[k.upper()].get(m.upper(), m.upper()), m.isupper()) for m, k in zip(message, cycle(key))
    )
  )

def decode(message: str, key: str) -> str:
  return ''.join(
    c if u else c.lower() for c, u in (
      (({v: k for k, v in table[k.upper()].items()}).get(m.upper(), m.upper()), m.isupper()) for m, k in zip(message, cycle(key))
    )
  )

if __name__ == '__main__':
  encode_key = "itmakesmehappy"
  message = "Hello, coins!!"

  assert "Pxxly, ospnh!!" == encode(message, encode_key)
  assert message == decode(encode(message, encode_key), encode_key)