input: Write a function to get the maximum and minimum values in a given list. The function should return a tuple containing the minimum and maximum values. If the list is empty, the function should return (None, None).
  
  def get_max_min(lst):
      if not lst:
          return (None, None)
      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)
  
  assert get_max_min([1, 2, 3, 4, 5])==(1, 5)
  assert get_max_min([5, 3, 7, 1])==(1, 7)
  assert get_max_min([-1, -2, -3, -4, -5])==(-5, -1)
  assert get_max_min([])==(None, None)
output: def get_max_min(lst):
      if not lst:
          return (None, None)
      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)