a gdk.Atom which identifies the clipboard to use. GDK_SELECTION_CLIPBOARD gives the default clipboard. Another common value is GDK_SELECTION_PRIMARY, which gives the primary X selection.
the appropriate clipboard object. If no clipboard already exists, a new one will be created. Once a clipboard object has been created, it is persistent for all time.
Returns the clipboard object for the given selection to be used with widget. widget must have a gdk.Display associated with it, so must be attached to a toplevel window.