ceasar

import argparse

parser = argparse.ArgumentParser(description="Vigenere cipher tool")

parser.add_argument('-e', '--encrypt', action='store_true', help='Encrypt ASCII message')
parser.add_argument('-d', '--decrypt', action='store_true' , help = "Decrypt ASCII message")

args = parser.parse_args()

def encrypt(plaintext, shift):
    ciphertext = ''
    for i in range(len(plaintext)):
        ciphertext += chr(ord(plaintext[i]) + shift % 26)
    print(ciphertext)

def decrypt(ciphertext, shift):
    plaintext = ''
    for i in range(len(ciphertext)):
        plaintext += chr(ord(ciphertext[i]) - shift % 26)
    print(plaintext)

def main():
    if args.encrypt:
        plaintext = raw_input('Enter plaintext: ').upper()
        shift = int(raw_input('Enter shift: '))
        encrypt(plaintext, shift)
    if args.decrypt:
        ciphertext = raw_input('Enter ciphertext: ').upper()
        shift = int(raw_input('Enter shift: '))
        decrypt(ciphertext, shift)

if __name__ == "__main__":
    main()