input: Write a function to find the greatest 2 numbers from a list of integers. The function should iterate through the list and keep track of the two largest numbers encountered. The function should return these two largest numbers as a tuple.
  
  def get_greatest_2(items):
   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([4, 3, 1, 2]) == (4, 3)
  assert get_greatest_2([3, 5, 7, 9, 11, 13, 15, 17, 19, 21]) == (21, 19)
  assert get_greatest_2([-1, -2, -3, -4, -5]) == (-1, -2)
  assert get_greatest_2([7]) == (7, float('-inf'))
output: def get_greatest_2(items):
      max1 = max2 = float('-inf')
      for item in items:
          if item > max1:
              max1, max2 = item, max1
          elif item > max2:
              max2 = item
      return max1, max2