Get the set of backup paths, given the virtualchain implementation module and block number

def get_backup_paths(cls, block_id, impl, working_dir):
        """
        Get the set of backup paths, given the virtualchain implementation module and block number
        """
        backup_dir = config.get_backups_directory(impl, working_dir)
        backup_paths = []
        for p in cls.get_state_paths(impl, working_dir):
            pbase = os.path.basename(p)
            backup_path = os.path.join( backup_dir, pbase + (".bak.%s" % block_id))
            backup_paths.append( backup_path )

        return backup_paths