Fix keepalives

Author: franzpoeschel

src/binding/python/Iteration.cpp

@@ -101,15 +101,15 @@ void init_Iteration(py::module &m)
                 py::return_value_policy::copy,
                 // garbage collection: return value must be freed before
                 // Iteration
-                py::keep_alive<1, 0>()))
+                py::keep_alive<0, 1>()))
         .def_property_readonly(
             "particles",
             py::cpp_function(
                 [](Iteration &i) { return i.particles; },
                 py::return_value_policy::copy,
                 // garbage collection: return value must be freed before
                 // Iteration
-                py::keep_alive<1, 0>()));
+                py::keep_alive<0, 1>()));
 
     add_pickle(
         cl, [](openPMD::Series series, std::vector<std::string> const &group) {

src/binding/python/ParticleSpecies.cpp

@@ -54,7 +54,7 @@ void init_ParticleSpecies(py::module &m)
                 [](ParticleSpecies &ps) { return ps.particlePatches; },
                 py::return_value_policy::copy,
                 // garbage collection: return value must be freed before Series
-                py::keep_alive<1, 0>()));
+                py::keep_alive<0, 1>()));
     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

@@ -503,7 +503,7 @@ this method.
                 [](Series &s) { return s.iterations; },
                 py::return_value_policy::copy,
                 // garbage collection: return value must be freed before Series
-                py::keep_alive<1, 0>()))
+                py::keep_alive<0, 1>()))
         .def(
             "read_iterations",
             [](Series &s) {