Encrypt and decrypt a given string with a given key number to a list of numbers string which can be recreated by using the same key number again

simpleCaesarForStrings.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def cipher(text, key):
    """ From https://stackoverflow.com/a/17984554/7827128 """

    return [(c + key) % 256 for c in text.encode('utf8')]


def decipher(data, key):
    """ From https://stackoverflow.com/a/17984554/7827128 """

    return bytes([(c - key) % 256 for c in data]).decode('utf8')


def encrypt(message, key):
    """ Encrypt a given string """

    print('Encrypt "' + message + '" with the key "' + str(key) + '"')
    print(' '.join(map(str, cipher(message, key))))


def decrypt(message, key):
    """ Decrypt a given string """

    print('Decrypt "' + message + '" with the key "' + str(key) + '"')
    try:
        print(decipher(map(int, message.split(' ')), key))
    except ValueError:
        print('Error: The message to decrypt is not a list of numbers!')
        return 0


def RepresentsInt(s):
    """ Check if the given string represents an integer """

    try:
        int(s)
        return True
    except ValueError:
        return False


def main():
    """ Main program """

    # Setup variables
    decryptBool = True
    message = ''
    key = False

    # Get the if to decrypt or encrypt
    for x in sys.argv:
        if str(x) == '-e':
            decryptBool = False
            break

    # Get the key
    for x in sys.argv:
        if RepresentsInt(x):
            key = int(x)
            break
    if not key:
        print('Error: No key found!')
        return 0

    # Get the message
    for x in sys.argv:
        if str(x) != '-e' and str(x) != '' and not str(x).endswith('.py') and str(x) != str(key):
            message = str(x)
            break
    if message == '':
        print('Error: No message found!')
        return 0

    # Check if decrypt or encrypt
    if decryptBool:
        decrypt(message, key)
    else:
        encrypt(message, key)

    # Quit successfully
    return 0


if __name__ == "__main__":
    """ To decrypt a message use as arguments: "encryptedString" keyNumber
    To encrypt a string use as arguments: -e "stringToEncrypt" keyNumber """

    main()