If focus is not the current focus widget, and is focusable, sets it as the
focus widget for the dialog.
If focus is NULL, unsets the focus widget for this dialog. To set the focus
to a particular widget in the dialog, it is usually more convenient to use
gtk.widget.Widget.grabFocus instead of this function.
Sets the focus widget for self.
If focus is not the current focus widget, and is focusable, sets it as the focus widget for the dialog.
If focus is NULL, unsets the focus widget for this dialog. To set the focus to a particular widget in the dialog, it is usually more convenient to use gtk.widget.Widget.grabFocus instead of this function.