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    Hi, I am currently trying to write a program, for school, in order to encrypt and de-rypt a inputted message. My code currently works but it is not fully complete. I am having trouble trying to allow it to enter an offset from values from 2-26 and I am having trouble making it repeat the question then carry on with the code until it gets the correct value. Right now it just says invalid message when a wrong number is entered but still carries on with the code. Also I need the encrypted or decrypted message to only be in the alphabet no other symbols or keys. Can anyone help please? This is my code currently.

    result = ''
    message = ''
    choice = ''

    offset=int(input("Enter an offset: "))
    if offset >25 or offset <0:
    print("Invalid offset, please enter another offset: ")

    while choice != '3':
    choice = input("\nDo you want to encrypt or decrypt the message?\nEnter 1 to Encrypt, 2 to Decrypt, 3 to Exit Program: ")

    if choice == '1':
    message = input("\nEnter the message to encrypt: ")

    for i in range(0, len(message)):
    result = result + chr(ord(message[i]) - offset)

    print (result + '\n\n')
    result = ''

    elif choice == '2':
    message = input("\nEnter the message to decrypt: ")

    for i in range(0, len(message)):
    result = result + chr(ord(message[i]) + offset)

    print (result + '\n\n')
    result = ''

    elif choice != '3':
    print ("You have entered an invalid choice. Please try again.\n\n")

    Go to StackOverflow and post this question. You'll get more responses there.
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