code: public PythonDataStream<SingleOutputStreamOperator<PyObject>> map(
  		MapFunction<PyObject, PyObject> mapper) throws IOException {
  		return new PythonSingleOutputStreamOperator(stream.map(new PythonMapFunction(mapper)));
  	}
docs: A thin wrapper layer over {@link DataStream#map(MapFunction)}.
  
  @param mapper The MapFunction that is called for each element of the
  DataStream.
  @return The transformed {@link PythonDataStream}.