def keys_output(mode, used_key_one, used_key_two, used_key_three):
    """
    Return the keys used for encryption or decryption,
    based on mode that was used.
    """
    if mode == "E":
        return print("Keys used for encryption were: '{}', '{}', '{}'.".format(
            used_key_one, used_key_two, used_key_three)
        )
    else:
        return print("Keys used for decryption were: '{}', '{}', '{}'.".format(
            used_key_one, used_key_two, used_key_three)
        )