Hello. I've been stuck on this assignment for awhile and can'tseem to figure out how to properly execute it. I've already donethe parts I can, the part I'm struggling with is adding exceptionhandling to the lines indicated.

import randomimport timedef countdown(n):    while n >= 0:        print n        time.sleep(1)        n -= 1# Self Destruct Custom Function# This is the custom function created to handle all of the Self Destruct# features needed. There are a few steps involved in the process, so take a few# moments to study how this function works and think about ways to make it better.def self_destruct(x):    # Set Destruct Codes    authorized_test = "000-Destruct-0"    authorized_final = "000-Destruct-1"    #  Display Self Destruct Warning    print "--------------------- WARNING! ----------------------"    print "You have initiated the USR ARES Self Destruct Program"    print "_____________________________________________________"    print "You must provide Authorized Initiate Code to Proceed."    # This next section of code is designed to prevent the user from entering the wrong information    while True:        try:            # Request Authorized Rank            rank = int(raw_input(                "Select Rank: [1] Commanding Officer [2] Executive Officer [3] Chief Engineer RANK: "))            # Because we're expecting the user to enter a number above, the conditional statement            # below is needed to convert those numbers into something more useful. Doing this helps            # reduce the risk of the user introducing bad data into the script.            # Retrieve Rank Initiate Code            if rank == 1:                code = "111A-Destruct"                print "Commanding Officer Confirmed."                break            # Executive Officer            elif rank == 2:                code = "21A2B-Destruct"                print "Executive Officer Confirmed."                break            # Chief Engineer            elif rank == 3:                code = "31B2B-Destruct"                print "Chief Engineer Confirmed."                break            else:                print "You are not authorized to initial Self Destruct."        except ValueError:            print "You have entered an invalid code. Please try again."    #######################################################################    # ADD EXCEPTION HANDLING TO THE FOLLOWING SECTION OF CODE             #    # The user must enter a correct code in order to proceed with the     #    # self destruct procedure.                                            #    #                                                                     #    # The script should force the user to enter a valid destruct code or  #    # or offer the option to abort the Self Destruct request entirely.    #    # Use the Exception Handling in the Section above as a reference.     #    #######################################################################    initiate = raw_input("Enter Self Destruct Confirmation Code: ")    # Compare Rank Codes    if initiate == code:            print "Self Destruct Initiate Code: ACCEPTED"            final_code = raw_input("Enter Activation Code: ")        if final_code == authorized_final:            print "Destruct Sequence Confirmed."            # 10. EXPLAIN THE SIGNIFICANCE OF THE str() FUNCTION HERE            print str(x) + " seconds to Self Destruct."            print "ALL HANDS ABANDON SHIP - THIS IS NOT A DRILL"            countdown(x)            print "Have a nice day!"            print "BOOM!"        elif final_code == authorized_test:            print "Destruct Sequence Test Order Confirmed."            print "THIS IS A DRILL - THIS IS A DRILL"            print "Timer Set to: " + str(x) + " seconds."        else:            print "Destruct Sequence Aborted."    ######################################################################## Self Destructtimer = int(raw_input("Enter Countdown Length (in seconds): "))self_destruct(timer)