'Change the child widget contained by this container widget.
:param child: The new child widget.  ``child`` must not have a
parent.
:type child: CanvasWidget
:rtype: None'

def set_child(self, child):

    self._remove_child_widget(self._child)
    self._add_child_widget(child)
    self._child = child
    self.update(child)
