Encryption and Decryption within the alphabet - Python GCSE

Question

I am currently trying to write a program, for school, in order to encrypt and decrypt a inputted message. I need the encrypted or decrypted message to only be in the alphabet no

Answer 1

def getOffset():
    offset = -1
    while not 0 < offset < 25:
        try: offset = int(input("Please enter an integer offset between 1 and 25: "))
        except ValueError: continue
    return offset


def encrypt(msg, offset):
    base = ord('a')
    chars = (ord(char)-base for char in msg)
    cipher = (base + ((c+offset)%26) for c in chars)
    return ''.join([chr(c) for c in cipher])


decrypt = lambda msg,offset: encrypt(msg, -offset)


def main():
    msg = """Please choose 
[1] to encrypt
[2] to decrypt
[3] to exit
"""

    funcs = {1: encrypt, 2: decrypt}

    while True:
        try: choice = int(input(msg))
        except ValueError: continue

        if choice == 3: return
        message = input("Please enter the message that you would like to {}: ".format(funcs[choice].__name__))
        offset = int(input("Please enter the offset: "))
        print(funcs[choice](message, offset))