code: def sign_items(self, sign_with):
          
          cart_items = self.items()
          item_paths = [item.path for item in cart_items]
          sign_with(item_paths)
  
          for item in cart_items:
              item.refresh()
docs: Sign the items in the cart with a GPG key.
  
          After everything is collected and signed all the cart items
          are issued a refresh() to sync their is_signed attributes.
  
          `sign_with` is a reference to the method that implements
          juicer.common.RpmSignPlugin.