There have been some changes to the rmf module that have some minor affects on how one would write assignments to a file or construct an assignment hdf5 container. The main difference is that to construct/open a data set for writing, you append _2d to the function call, rather than pass an argument of 2. eg data_set= rt.add_child_index_data_set_2d("node_1_assignments")

If you do it in C++, the data set type is now ::rmf::HDF5IndexDataSet2D or ::rmf::HDF5DataSetD<::rmf::IndexTraits, 2>.