def __setitem__(self, key, value):
        """
            Override this method to ensure that only valid filesystem
            objects are added. Raises ValueError if not.
            
        """
        if not os.path.exists(value):
            raise ValueError, ("Item not found on file system: %s"% value)
        else:
            super(FSList, self).__setitem__(key, value)

            Override this method to ensure that only valid filesystem
            objects are added. Raises ValueError if not.
            
        
recipes/Python/259147_FSList/recipe-259147.py