input: 
  def third_largest(lst):
      if len(lst) < 3:
          return
      distinct = []
      for i in lst:
          if i not in distinct:
              distinct.append(i)
      distinct.sort(reverse=True)
      return distinct[2]
  
  """
  Get the third largest element in a given list.
  >>> third_largest([12, 13, 13, 45, 22, 99])
  22
  """
  
output:     if len(distinct) < 3:
          return
      return distinct[2]