Dynamic menus question

["Christian Convey" <christian convey gmail com>]

I'm using pygtk.  My top-level menubar has a menuitem named "Scripts".
Each time user clicks on "Scripts", I want a chance to update the
Scripts menuitem's submenu content before it's shown to the user. That
way the submenu's content will alway be up-to-date when it's presented
to the user.

I'm having trouble identifying the widget,signal combination that
triggers (a) sometime after the user clicks on "Scripts" in the menu
bar, but (b) before it's too late to modify the content the Script
menuitem's submenu.

And idea what signal/widget I should attach the code to that does the update?

Thanks,
Christian