docs: 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