NameError: name 'ShapeNode' is not defined

Hi, Michael. 
I run this script and get the error. 

`Traceback (most recent call last):
  File "E:/test/2.py", line 37, in <module>
    class cuboid(ShapeNode):
NameError: name 'ShapeNode' is not defined`

How can I solve this problem?

Thinks.