input: 
  def get_max_min(lst):
      """ Returns a tuple of the maximum and minimum values in a given list.
      >>> get_max_min([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])
      (1, 9)
      >>> get_max_min([-10, 0, 10, 20])
      (-10, 20)
      """
      min_value = lst[0]
      max_value = lst[0]
      
      for i in range(1, len(lst)):
          if lst[i] > max_value:
              max_value = lst[i]
          if lst[i] < min_value:
              min_value = lst[i]
      
      return (min_value, max_value)
  
output:     min_value = lst[0]
      max_value = lst[0]
      
      for i in range(1, len(lst)):
          if lst[i] > max_value:
              max_value = lst[i]
          if lst[i] < min_value:
              min_value = lst[i]
      
      return (min_value, max_value)