super_list("first level", 5, ..., 9, array.move_up, array.move_up, "second level", 10, ..., 15, array.move_down, "down one level")

['first level', 5, 6, 7, 8, 9, [['second level', 10, 11, 12, 13, 14, 15], 'down one level']]

def get_in_list(lst, indexes):
  """Gets an item in a nested list by a list of indexes."""
  return functools.reduce(operator.getitem, indexes, lst)

def super_list(*args):
  """Special initialization syntax for lists."""
  curr_index = []
  result = []
  for index, item in enumerate(args): # Iterate over args with indexes
    el_type = type(...) # Type of the Ellipsis object
    if isinstance(item, el_type): # Case: Ellipsis range generator
      if index == 0:
        get_in_list(result, curr_index).append(item)
      else:
        get_in_list(result, curr_index).extend(list(range(args[index-1]+1, args[index+1])))
    elif item == array.move_up: # Case: move up one level in list
      get_in_list(result, curr_index).append([])
      curr_index.append(len(get_in_list(result, curr_index))-1)
    elif item == array.move_down: # Case: move down one level in list
      try:
        curr_index.pop()
      except IndexError: # Silently catch if user tries to move down too far in the list
        pass
    else: # Case: No special syntax - regularly append item to list
      get_in_list(result, curr_index).append(item)
  return result