code: def add_child(self, child):
          
          if not issubclass(child.__class__, SceneGraph):
              raise TypeError("child must have parent/child iteration implemented to be a node in a SceneGraph.")
          # if not hasattr(child, 'update'):
              # raise TypeError("child must have an attribute update()")
  
          child._parent = self
          self._children.append(child)
docs: Adds an object as a child in the scene graph.