Causes widget to have the keyboard focus for the gtk.Window it's inside. widget must be a focusable widget, such as a gtk.Entry; something like gtk.Frame won’t work.

More precisely, it must have the GTK_CAN_FOCUS flag set. Use Widget.setCanFocus to modify that flag.

The widget also needs to be realized and mapped. This is indicated by the related signals. Grabbing the focus immediately after creating the widget will likely fail and cause critical warnings.

class Widget