func_code: def search(str, letter):
      if len(str) == 0:
          return False
      elif str[0] == letter:
          return True
      else:
          return search(str[1:], letter)
  
  
  def index(str, letter):
      if len(str) == 0:
          return -1
      elif str[len(str)] == letter:
          return len(str)
      else:
          return search(str[:len(str)], letter)