def get_offset(c):
    # uses Python inline if: http://stackoverflow.com/questions/11880430/how-to-write-inline-if-statement-for-print
    return 65 if c.isupper() else 97

def encrypt_char(c, key):
    offset = get_offset(c)
    return chr(((ord(c) - offset + key) % 26) + offset)

def decrypt_char(c, key):
    offset = get_offset(c)
    ordinal = ord(c) - offset - key + 26 if ((ord(c) - offset) < key) else (ord(c) - offset - key)
    return chr((ordinal % 26) + offset)

def vigenere(message, key, encrypt=True):
    op = encrypt_char if encrypt else decrypt_char
    key = [ord(c) - get_offset(c) for c in key]
    def vigenere_helper(message, key_index, ciphertext, op):
        return ciphertext if message == '' else vigenere_helper(message[1:], (key_index + 1) % len(key),
                    ciphertext + (op(message[0], key[key_index]) if message[0].isalpha() else message[0]), op)
    return vigenere_helper(message, 0, '', op)