Tryout for Caesar Crypt (maybe a salad is better)

import argparse
import sys

# Define main variables
list1 = []
list2 = []
list3 = []


def get_args():
    parser = argparse.ArgumentParser(
        description="""Caesar Encoder/Decoder""")
    parser.add_argument(
        '-a', '--action', type=str, choices=['encrypt', 'decrypt'], required=True)
    parser.add_argument(
        '-s', '--shift', type=int, help='Char. shift number', required=True)
    parser.add_argument(
        'input_string', nargs='+', help='string to encrypt/decrypt')
    terminal_args = parser.parse_args()
    return terminal_args

#TODO: limit args.shift range to 26
def args_check():
    args = get_args()
    if args.input_string != "":
        return args
    else:
        print(str("Incorrect arguments passed on"))
        sys.exit()

def normalize_input(string):
    string = string.upper()
    return string

# Cypher function
def cipher_this(string, cypher_shift):
    string = normalize_input(string)
    print(str("Input to encode is: ") + string)
    # Generate list1 from unicode string
    for letter in string:
        list1.append((ord(letter)))

    # From list1, add cypher shift to the list
    for element in list1:
        list2.append(cypher_shift + element)

    # convert list2 onto coded string
    for element in list2:
        list3.append(str(chr(element)))
        cyph_text = ''.join(list3)
    print(str("Encoded output is : ") + cyph_text)

def decipher_this(string, cypher_shift):
    string = normalize_input(string)
    print(str("Input to decode is: ") + string)
    # Generate list1 from unicode string
    for letter in string:
        list1.append((ord(letter)))

    # From list1, add cypher shift to the list
    for element in list1:
        list2.append(element - cypher_shift)

    # convert list2 onto coded string
    for element in list2:
        list3.append(str(chr(element)))
        cyph_text = ''.join(list3)
    print(str("Decoded output is : ") + cyph_text)


def main():
    print(str("Caesar Salad begin..."))
    args = args_check()
    string = str(args.input_string).strip("\'[]")
    shift = int(args.shift)
    action_to_do = str(args.action).strip("\'[]")
    if action_to_do == "encrypt":
        cipher_this(string, shift)
    else:
        decipher_this(string, shift)

if __name__ == "__main__":
    main()