code: def init_layout(self):
          
          widget = self.widget
          for child_widget in self.child_widgets():
              widget.addSubview(child_widget)
docs: Initialize the layout of the toolkit widget.
  
           This method is called during the bottom-up pass. This method
           should initialize the layout of the widget. The child widgets
           will be fully initialized and layed out when this is called.