code: def GetDataStreamByPathSpec(self, path_spec):
      
      file_entry = self.GetFileEntryByPathSpec(path_spec)
      if not file_entry:
        return None
  
      data_stream_name = getattr(path_spec, 'data_stream', None)
      return file_entry.GetDataStream(data_stream_name)
docs: Retrieves a data stream for a path specification.
  
      Args:
        path_spec (PathSpec): a path specification.
  
      Returns:
        DataStream: a data stream or None if not available.