import string def decryption(encryption, key: int): uppercase = string.ascii_uppercase lowercase = string.ascii_lowercase decrypt = "" for c in encryption: if c in uppercase: index = (uppercase.index(c) - key) % 26 decrypt += uppercase[index] if c in lowercase: index = (lowercase.index(c) - key) % 26 decrypt += lowercase[index] if (c not in uppercase) and (c not in lowercase): decrypt += c return decrypt a_str = "pb qdph lv Jdlxv Lxolxv Fdhvdu." print(decryption(a_str, 3))