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