def save_state(self, fname):
        """
        Save the state of this node (the alpha/ksize/id/immediate neighbors)
        to a cache file with the given fname.
        """
        log.info("Saving state to %s", fname)
        data = {
            'ksize': self.ksize,
            'alpha': self.alpha,
            'id': self.node.id,
            'neighbors': self.bootstrappable_neighbors()
        }
        if not data['neighbors']:
            log.warning("No known neighbors, so not writing to cache.")
            return
        with open(fname, 'wb') as file:
            pickle.dump(data, file)
Save the state of this node (the alpha/ksize/id/immediate neighbors)
        to a cache file with the given fname.