Causes widget to become the default widget. widget must be able to be a default widget; typically you would ensure this yourself by calling Widget.setCanDefault with a TRUE value. The default widget is activated when the user presses Enter in a window. Default widgets must be activatable, that is, Widget.activate should affect them. Note that gtk.Entry widgets require the “activates-default” property set to TRUE before they activate the default widget when Enter is pressed and the gtk.Entry is focused.