def METHOD_NAME(self, notebook, page, page_num):
    """
    Handle a page change. When the user clicks on a new tab,
    reload the flow graph to update the vars window and
    call handle states (select nothing) to update the buttons.
    Args:
        notebook: the notebook
        page: new page
        page_num: new page number
    """
    self.current_page = self.get_nth_page(page_num)
    Actions.PAGE_CHANGE()