input: Write a function to find the largest three numbers in a given list. If the list has fewer than three numbers, return all the numbers in the list. Return the result in descending order.
  assert largest_three([1, 6, 3, 8, 7, 4])==[8, 7, 6]
  assert largest_three([5, 2, 9])==[9, 5, 2]
  assert largest_three([10])==[10]
  assert largest_three([3, 4])==[4, 3]
  assert largest_three([])==[]
output: def largest_three(nums):
      return sorted(nums, reverse=True)[:3]