code: def FromStream(cls, stream):
          
  
          if stream.system:
              specifier = DataStreamSelector.MatchSystemOnly
          else:
              specifier = DataStreamSelector.MatchUserOnly
  
          return DataStreamSelector(stream.stream_type, stream.stream_id, specifier)
docs: Create a DataStreamSelector from a DataStream.
  
          Args:
              stream (DataStream): The data stream that we want to convert.