input: Write a function to find the greatest 2 numbers from a list of integers. The function should return a tuple containing the two greatest numbers in descending order. If the list has less than two elements, the function should return a tuple containing the greatest number and None.
  
  def get_greatest_2(items):
      if len(items) < 2:
          return (max(items), None)
      max1 = max2 = float('-inf')
      for item in items:
          if item > max1:
              max1, max2 = item, max1
          elif item > max2:
              max2 = item
      return max1, max2
  
  assert get_greatest_2([1, 5, 3, 7, 4, 7, 8, 9, 2, 10, 6, 8]) == (10, 9)
  assert get_greatest_2([1, 2]) == (2, 1)
  assert get_greatest_2([5]) == (5, None)
  assert get_greatest_2([]) == (None, None)
output: def get_greatest_2(items):
      if len(items) < 2:
          return (max(items, default=None), None)
      max1 = max2 = float('-inf')
      for item in items:
          if item > max1:
              max1, max2 = item, max1
          elif item > max2:
              max2 = item
      return max1, max2