'Show the page whose name is given in page_name.'

def change_page(self, page_name):

    if (self._current_page == page_name):
        return
    if ((page_name is not None) and (page_name not in self.pages)):
        raise KeyError(("No    such    TabPage:    '%s'" % page_name))
    if (self._current_page is not None):
        self.pages[self._current_page]._hide()
    self._current_page = None
    if (page_name is not None):
        self._current_page = page_name
        self.pages[page_name]._show()
    self._tab_set.set_selected_tab(page_name)
