caesar python version

caesar.py

import sys

if len(sys.argv) != 2: 
  print("Usage: python3 caesar.py key")
  sys.exit(0)
key = int(sys.argv[1])

message = input("enter a secret message: ")

def cipher(letter, key):
	if not letter.isalpha():
		return letter
	offset = 65 if letter.isupper() else 97
	return chr(((ord(letter) - offset) + key) % 26 + offset)

print(f"userinput: {message}")
print("decoded_text: " + ''.join([cipher(letter, key * -1) for letter in message]))
print("coded_text: " + ''.join([cipher(letter, key) for letter in message]))