input: Write a python function to find the largest and smallest numbers in a list.
  assert find_largest_smallest([9, 10, -12, 0, 5]) == (10, -12)
  assert find_largest_smallest([1, 2, 3, 4, 5]) == (5, 1)
  assert find_largest_smallest([-1, -2, -3, -4, -5]) == (-1, -5)
output: def find_largest_smallest(lst):
      if not lst:
          return None, None
      largest = max(lst)
      smallest = min(lst)
      return largest, smallest