code: def _active_todos(self):
          
          return [todo for todo in self.todolist.todos()
                  if not self._uncompleted_children(todo) and todo.is_active()]
docs: Returns a list of active todos, taking uncompleted subtodos into
          account.
  
          The stored length of the todolist is taken into account, to prevent new
          todos created by recurrence to pop up as newly activated tasks.
          Since these todos pop up at the end of the list, we cut off the list
          just before that point.