Generates callback (which called by accel key) to go to the Nth tab.

def gen_accel_switch_tabN(self, N):
        """Generates callback (which called by accel key) to go to the Nth tab.
        """

        def callback(*args):
            if 0 <= N < self.get_notebook().get_n_pages():
                self.get_notebook().set_current_page(N)
            return True

        return callback