'Show the tab named <tab_name> as the selected one'

def set_selected_tab(self, tab_name):

    if (tab_name == self._selected_tab):
        return
    else:
        if ((tab_name is not None) and (tab_name not in self._tabs)):
            raise KeyError(("No    such    Tab:    '%s" % page_name))
        if (self._selected_tab is not None):
            self._tabs[self._selected_tab].set_normal()
        self._selected_tab = None
        if (tab_name is not None):
            self._selected_tab = tab_name
            tab = self._tabs[tab_name]
            tab.set_selected()
            tab_row = self._tab2row[tab]
            tab_row.pack_forget()
            tab_row.pack(side=TOP, fill=X, expand=0)
        return
