Can someone help me solve this string index error in python? -

this code need schools cau, thought had solved keep getting string index error, wondering if tell me whyerror message

letters = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n","o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]  menu = """  caesar cipher ======================================================== |  exit program ---------------------- enter 0  |  |  find lucky name number ----------- enter 1  | \------------------------------------------------------/ """ option = ""  def lucky_name():     forename = input("what forename?") surname = input("what surname?") forenaem = str(forename) surnamenum = 0 forenamenum = 0 luckynum = 0 forename = str (forename) surname = str (surname) totalnum = 0  while totalnum <= len(forename):     if forename[totalnum] == letters[0]:         forenamenum = forenamenum + 1    elif forename[totalnum] == letters[1]:         forenamenum = forenamenum + 2    elif forename[totalnum] == letters[2]:         forenamenum = forenamenum + 3    elif forename[totalnum] == letters[3]:         forenamenum = forenamenum + 4       elif forename[totalnum] == letters[4]:         forenamenum = forenamenum + 5    elif forename[totalnum] == letters[5]:         forenamenum = forenamenum + 6    elif forename[totalnum] == letters[6]:         forenamenum = forenamenum + 7    elif forename[totalnum] == letters[7]:         forenamenum = forenamenum + 8    elif forename[totalnum] == letters[8]:         forenamenum = forenamenum + 9    elif forename[totalnum] == letters[9]:         forenamenum = forenamenum + 1    elif forename[totalnum] == letters[10]:         forenamenum = forenamenum + 2    elif forename[totalnum] == letters[11]:         forenamenum = forenamenum + 3    elif forename[totalnum] == letters[12]:         forenamenum = forenamenum + 4    elif forename[totalnum] == letters[13]:         forenamenum = forenamenum + 5    elif forename[totalnum] == letters[14]:         forenamenum = forenamenum + 6    elif forename[totalnum] == letters[15]:         forenamenum = forenamenum + 7    elif forename[totalnum] == letters[16]:         forenamenum = forenamenum + 8    elif forename[totalnum] == letters[17]:         forenamenum = forenamenum + 9    elif forename[totalnum] == letters[18]:         forenamenum = forenamenum + 1    elif forename[totalnum] == letters[19]:         forenamenum = forenamenum + 2    elif forename[totalnum] == letters[20]:         forenamenum = forenamenum + 3    elif forename[totalnum] == letters[21]:         forenamenum = forenamenum + 4    elif forename[totalnum] == letters[22]:         forenamenum = forenamenum + 5    elif forename[totalnum] == letters[23]:         forenamenum = forenamenum + 6    elif forename[totalnum] == letters[24]:         forenamenum = forenamenum + 7    elif forename[totalnum] == letters[25]:         forenamenum = forenamenum + 8    totalnum = totalnum + 1   totalnum2 = 0     while totalnum2 <= len(surname):     if surname[totalnum2] == letters[0]:         surnamenum = surnamenum + 1         elif surname[totalnum2] == letters[1]:         surnamenum = surnamenum + 2     elif surname[totalnum2] == letters[2]:         surnamenum = surnamenum + 3     elif surname[totalnum2] == letters[3]:         surnamenum = surnamenum + 4     elif surname[totalnum2] == letters[4]:         surnamenum = surnamenum + 5     elif surname[totalnum2] == letters[5]:         surnamenum = surnamenum + 6     elif surname[totalnum2] == letters[6]:         surnamenum = surnamenum + 7     elif surname[totalnum2] == letters[7]:         surnamenum = surnamenum + 8     elif surname[totalnum2] == letters[8]:         surnamenum = surnamenum + 9     elif surname[totalnum2] == letters[9]:         surnamenum = surnamenum + 1     elif surname[totalnum2] == letters[10]:         surnamenum = surnamenum + 2     elif surname[totalnum2] == letters[11]:         surnamenum = surnamenum + 3     elif surname[totalnum2] == letters[12]:         surnamenum = surnamenum + 4     elif surname[totalnum2] == letters[13]:         surnamenum = surnamenum + 5     elif surname[totalnum2] == letters[14]:         surnamenum = surnamenum + 6     elif surname[totalnum2] == letters[15]:         surnamenum = surnamenum + 7     elif surname[totalnum2] == letters[16]:         surnamenum = surnamenum + 8     elif surname[totalnum2] == letters[17]:         surnamenum = surnamenum + 9     elif surname[totalnum2] == letters[18]:         surnamenum = surnamenum + 1     elif surname[totalnum2] == letters[19]:         surnamenum = surnamenum + 2     elif surname[totalnum2] == letters[20]:         surnamenum = surnamenum + 3     elif surname[totalnum2] == letters[21]:         surnamenum = surnamenum + 4     elif surname[totalnum2] == letters[22]:         surnamenum = surnamenum + 5     elif surname[totalnum2] == letters[23]:         surnamenum = surnamenum + 6     elif surname[totalnum2] == letters[24]:         surnamenum = surnamenum + 7     elif surname[totalnum2] == letters[25]:         surnamenum = surnamenum + 8     totalnum2 = totalnum2 + 1  forenamenum = str(forenamenum) num1 = forenamenum[0] num2 = forenamenum[1] num1 = int(num1) num2 = int(num2) forenamenum = num1 + num2  surnamenum = str(surnamenum) num3 = surnamenum[0] num4 = surnamenum[1] num3 = int(num3) num4 = int(num4) surnamenum = num3 + num4  luckynum = surnamenum + forenamenum  if luckynum >= 10:     luckynum = str(luckynum)     num5 = luckynum[0]     num6 = luckynum[1]     num5 = int(num5)     num6 = int(num6)     luckynum = num5 + num6   print ("your name is:")  print ("your lucky number is:") print (luckynum)    return 

while not option == "0": print(menu) option = input("which option use? ")

if option == "0":     print("goodbye!")  elif option == "1":     lucky_name()  elif option == "2":     print("whoops. menu option doesn't exist.")     print("please try again.") 

your code wrong in while totalnum <= len(forename):

the len of array returns lenght of array starting 1 not 0.

if have [1,2,3] len 3 last position 2.

so solve problem change this:

while totalnum < len(forename):