code: def secured_clipboard(item):
      
      expire_clock = time.time()
      def set_text(clipboard, selectiondata, info, data):
          # expire after 15 secs
          if 15.0 >= time.time() - expire_clock:
              selectiondata.set_text(item.get_secret())
              clipboard.clear()
      def clear(clipboard, data):
          """Clearing of the buffer is deferred this only gets called if the 
          paste is actually triggered
          """
          pass
      targets = [("STRING", 0, 0)
                ,("TEXT", 0, 1)
                ,("COMPOUND_TEXT", 0, 2)
                ,("UTF8_STRING", 0, 3)]
      cp = gtk.clipboard_get()
      cp.set_with_data(targets, set_text, clear)
docs: This clipboard only allows 1 paste