Use cpp_function instead (.def(...))

These lose the setters, but those were not used anyway?
bit of an ugly workaround

Author: franzpoeschel

src/binding/python/Iteration.cpp

@@ -94,19 +94,18 @@ void init_Iteration(py::module &m)
         .def("set_dt", &Iteration::setDt<double>)
         .def("set_time_unit_SI", &Iteration::setTimeUnitSI)
 
-        // .def_readwrite(
-        //     "meshes",
-        //     &Iteration::meshes,
-        //     py::return_value_policy::copy,
-        //     // garbage collection: return value must be freed before Iteration
-        //     py::keep_alive<1, 0>())
-        // .def_readwrite(
-        //     "particles",
-        //     &Iteration::particles,
-        //     py::return_value_policy::copy,
-        //     // garbage collection: return value must be freed before Iteration
-        //     py::keep_alive<1, 0>())
-        ;
+        .def(
+            "__meshes",
+            [](Iteration &i) { return i.meshes; },
+            py::return_value_policy::copy,
+            // garbage collection: return value must be freed before Iteration
+            py::keep_alive<1, 0>())
+        .def(
+            "__particles",
+            [](Iteration &i) { return i.particles; },
+            py::return_value_policy::copy,
+            // garbage collection: return value must be freed before Iteration
+            py::keep_alive<1, 0>());
 
     add_pickle(
         cl, [](openPMD::Series series, std::vector<std::string> const &group) {

src/binding/python/ParticleSpecies.cpp

@@ -48,13 +48,12 @@ void init_ParticleSpecies(py::module &m)
               return stream.str();
           })
 
-        // .def_readwrite(
-        //     "particle_patches",
-        //     &ParticleSpecies::particlePatches,
-        //     py::return_value_policy::copy,
-        //     // garbage collection: return value must be freed before Series
-        //     py::keep_alive<1, 0>())
-        ;
+        .def(
+            "__particle_patches",
+            [](ParticleSpecies &ps) { return ps.particlePatches; },
+            py::return_value_policy::copy,
+            // garbage collection: return value must be freed before Series
+            py::keep_alive<1, 0>());
     add_pickle(
         cl, [](openPMD::Series series, std::vector<std::string> const &group) {
             uint64_t const n_it = std::stoull(group.at(1));

src/binding/python/Series.cpp

@@ -497,12 +497,12 @@ this method.
         .def("set_iteration_format", &Series::setIterationFormat)
         .def("set_name", &Series::setName)
 
-        // .def_readwrite(
-        //     "iterations",
-        //     &Series::iterations,
-        //     py::return_value_policy::copy,
-        //     // garbage collection: return value must be freed before Series
-        //     py::keep_alive<1, 0>())
+        .def(
+            "__iterations",
+            [](Series &s) { return s.iterations; },
+            py::return_value_policy::copy,
+            // garbage collection: return value must be freed before Series
+            py::keep_alive<1, 0>())
         .def(
             "read_iterations",
             [](Series &s) {

src/binding/python/openpmd_api/__init__.py

@@ -16,6 +16,10 @@
 Record_Component.to_dask_array = record_component_to_daskarray  # noqa
 Series.to_df = iterations_to_dataframe  # noqa
 Series.to_cudf = iterations_to_cudf  # noqa
+Series.iterations = property(Series.__iterations)
+Iteration.meshes = property(Iteration.__meshes)
+Iteration.particles = property(Iteration.__particles)
+ParticleSpecies.particle_patches = property(ParticleSpecies.__particle_patches)
 
 # TODO remove in future versions (deprecated)
 Access_Type = Access  # noqa