input: 
  def get_greatest_2(items):
      """
      Given a list of integers, find and return the greatest two numbers from the list.
      If the list contains fewer than two numbers, the function should return None.
      
      >>> get_greatest_2([1, 5, 3, 7, 4, 7, 8, 9, 2, 10, 6, 8])
      (10, 9)
      >>> get_greatest_2([20, 15, 30, 25, 40, 35])
      (40, 35)
      """
      if len(items) < 2:
          return None
      max1 = max2 = float('-inf')
      for item in items:
          if item > max1:
              max1, max2 = item, max1
          elif item > max2:
              max2 = item
      return max1, max2
  
output:     if len(items) < 2:
          return None
      max1 = max2 = float('-inf')
      for item in items:
          if item > max1:
              max1, max2 = item, max1
          elif item > max2:
              max2 = item
      return max1, max2