Python 3DES String Encryption & Decryption

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#==============MODULES================#
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from Crypto.Cipher import *
from Crypto import Random
import base64

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#==============VARIABLES==============#
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modes = ["(1) ECB    ", "(2) CBC    ", "(3) CFB    "]
mtypes = ["(1) Encrypt", "(2) Decrypt", "(3) Exit   "]
block_size = 8
key_size = 16
iv_size = 8

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#==============FUNCTIONS==============#
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#create menu
def menu(parameter):
        print "         +===========+"
        print "         |    MENU   |"
        print "         |-----------|"
        for word in parameter:
                print "         |%s|" % word
                print "         |-----------|"

#defines encryption algorithm
def enc(key_size, block_size, iv_size, mode):

        #get key and pad if necessary
        key = raw_input("Please enter a key: ")
        key += (key_size - len(key) % key_size) * chr(key_size - len(key) % key_size)

        #get data and pad if necessary
        data = raw_input("Please enter a string to encrypt: ")
        pad = lambda data: data + (block_size - len(data) % block_size) * chr(block_size - len(data) % block_size)
        data = pad(data)

        #generate random IV
        iv = Random.new().read(iv_size)

        #define what is needed for DES
        cipher = DES3.new(key, mode, iv)

        #combine IV and encrypted text | encode using base64
        output = base64.b64encode(iv + cipher.encrypt(data))

    print "The encrypted message is: ", output

#defines decryption algorithm
def dec(key_size, block_size, iv_size, mode):

        #get key and pad if necessary
        key = raw_input("Please enter a key: ")
        key += (key_size - len(key) % key_size) * chr(key_size - len(key) % key_size)

        #get data and decode base64
        data = raw_input("Please enter a string to decrypt: ")
        data = base64.b64decode(data)

        #get IV
        iv = data[:iv_size]

        #strip padding
        strippad = lambda data: data[0:-ord(data[-1])]

        #define what is needed for DES
        cipher = DES3.new(key, mode, iv)

        #strip off padding and decrypt data
        output = strippad(cipher.decrypt(data[iv_size:]))

        print "The decrypted message is: ", output

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#===========MAIN PROGRAM==============#
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def main():
    menu(mtypes)
    mtypes_choice = input("Please select to encrypt, decrypt, or exit(1-3): ")

    #Encryption
    if mtypes_choice == 1:
        menu(modes)
        menus_choice = input("Please select a mode of encryption(1-3): ")

        if menus_choice == 1:
            mode = DES3.MODE_ECB
            enc(key_size, iv_size, block_size, mode)
        elif menus_choice == 2:
            mode = DES3.MODE_CBC
            enc(key_size, iv_size, block_size, mode)
        elif menus_choice == 3:
            mode = DES3.MODE_CFB
            enc(key_size, iv_size, block_size, mode)

    #Decryption
    elif mtypes_choice == 2:
        menu(modes)
        menus_choice = input("Please select a mode of encryption(1-3): ")

        if menus_choice == 1:
            mode = DES3.MODE_ECB
            dec(key_size, iv_size, block_size, mode)
        elif menus_choice == 2:
            mode = DES3.MODE_CBC
            dec(key_size, iv_size, block_size, mode)
        elif menus_choice == 3:
            mode = DES3.MODE_CFB
            dec(key_size, iv_size, block_size, mode)

    #Exit
    elif mtypes_choice == 3:
        print "Exiting Program. Goodbye."
        print
        return

    #Fault
    else:
        print "ERROR. Invalid Selection."
        print
        print
        return main()