A python script that implements the vigenere cipher in one line, either as a function (vigeny.py) or as a standalone program (oneln.py).

import vigeny

message = 'FRIENDSROMANSCOUNTRYMENLENDMEYOUREARS'
key =     'KEYPHRASEKEYPHRASEKEYPHRASEKEYPHRASEK'

print('Encrypting ' + message + ' with the key ' + key)
cipherText = vigeny.crypt(message, key, 1)
print(cipherText)

print('Decyrpting ' + cipherText + ' with the key ' + key)
plainText = vigeny.crypt(cipherText, key, -1)
print(plainText)

As you can see the only function in vigeny is crypt. The first argument is the message or cipher text, the second argument is the key and then the third argument tells the function how to apply the key.

When the third argument is 1 the key is applied once, 2 it is applied twice etc. To decrypt simply set the third argument to the negative counter part of the one used to decrypt.
For example...
vigeny.crypt(message, key, 9) can be reversed with vigeny.crypt(message, key, -9)
and likewise...
vigeny.crypt(message, key, -4) can be reversed with vigeny.crypt(message, key, 4)

There is also a truly one line implementation that will run on its own in oneln.py.