A error happened in python, wenn use Class

Hey, everyone!
did anyone know, why I can not get the “Panels” in Python, like the Picture

Panels.append(yourItem). This is Python syntax actually…

Thanks ,Tom!
I know that .append is add a new item to a list.
But I am the first time to use “Class” and the ghpython is now always the puzzle for me.
Anyways Thank you so much