input: from typing import List, Tuple
  
  def get_max_min(lst: List[int]) -> Tuple[int, int]:
      """
      Get the maximum and minimum values in a given list.
      
      >>> get_max_min([3, 5, 1, 9, 2])
      (1, 9)
      >>> get_max_min([-10, 0, 10, -5])
      (-10, 10)
      >>> get_max_min([4])
      (4, 4)
      """
output:     if not lst:
          return (None, None)
      
      max_val = min_val = lst[0]
      
      for num in lst:
          if num > max_val:
              max_val = num
          if num < min_val:
              min_val = num
      
      return (min_val, max_val)