Python - Caesar Cipher

caesar_cipher.py

#!/usr/bin/python3
# Caesar Cipher

LEN,UP_MIN,LOW_MIN = 26,65,97

def getchar(ch, key, enc):
    if not ch.isalpha():
        return ch
    key = key if enc else -key
    (min,max) = (UP_MIN, UP_MIN+LEN) if ch.isupper() else (LOW_MIN, LOW_MIN+LEN)
    idx = ord(ch) + key
    mul = 1 if idx < min else (-1 if idx > max else 0)
    return chr(idx + mul * LEN)

def encdec(message, key, enc):
    result=[]
    for i in message:
        result.append(getchar(i,key,enc))
    return ''.join(result)
    
print('Enter the message : ', end='')
message,key=input(),0
while not (key > 0 and key < LEN):
    print('Enter key [1-26]  : ', end='')
    key=int(input())
encMsg = encdec(message, key, True)
print('Encrypted message : %s' % encMsg)
decMsg = encdec(encMsg, key, False)
print('Decrypted message : %s' % decMsg)