code: def CacheFileSystem(self, path_spec, file_system):
      
      identifier = self._GetFileSystemCacheIdentifier(path_spec)
      self._file_system_cache.CacheObject(identifier, file_system)
docs: Caches a file system object based on a path specification.
  
      Args:
        path_spec (PathSpec): path specification.
        file_system (FileSystem): file system object.