input: Write a function to get the maximum and minimum values in a given list. If the list is empty, return (None, None).
  def get_max_min(lst):
   if len(lst) == 0:
    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([-1, -2, -3, -4, -5]) == (-5, -1)
  assert get_max_min([]) == (None, None)
  assert get_max_min([7]) == (7, 7)
output: def get_max_min(lst):
   if len(lst) == 0:
    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)