Yield ownership of vector<double>, vector<float>, and vector<int> to mjSpec in Python bindings.

Fixes #2756

PiperOrigin-RevId: 785417251
Change-Id: Ib399c46ee59585258ace7d9583c68b7d06d0a9e4

python/mujoco/codegen/generate_spec_bindings.py

@@ -193,7 +193,7 @@ def _ptr_binding_code(
       []({rawclassname}& self, std::string_view {varname}) {{
         *(self.{fullvarname}) = {varname};
     }});"""
-  elif (  # C++ vectors of values -> Python array
+  elif (  # C++ vectors of values -> custom array
       vartype == 'mjDoubleVec'
       or vartype == 'mjFloatVec'
       or vartype == 'mjIntVec'
@@ -202,9 +202,9 @@ def _ptr_binding_code(
     return f"""\
   {classname}.def_property(
     "{varname}",
-    []({rawclassname}& self) -> py::array_t<{vartype}> {{
-        return py::array_t<{vartype}>(self.{fullvarname}->size(),
-                                      self.{fullvarname}->data());
+    []({rawclassname}& self) -> MjTypeVec<{vartype}> {{
+        return MjTypeVec<{vartype}>(self.{fullvarname}->data(),
+                                    self.{fullvarname}->size());
       }},
     []({rawclassname}& self, py::object rhs) {{
         self.{fullvarname}->clear();
@@ -212,7 +212,7 @@ def _ptr_binding_code(
         for (auto val : rhs) {{
           self.{fullvarname}->push_back(py::cast<{vartype}>(val));
       }}
-    }}, py::return_value_policy::reference_internal);"""
+    }}, py::return_value_policy::move);"""
   elif vartype == 'mjByteVec':
     return f"""\
   {classname}.def_property(

python/mujoco/specs.cc

@@ -221,6 +221,9 @@ PYBIND11_MODULE(_specs, m) {
   DefineArray<char>(m, "MjCharVec");
   DefineArray<std::string>(m, "MjStringVec");
   DefineArray<std::byte>(m, "MjByteVec");
+  DefineArray<double>(m, "MjDoubleVec");
+  DefineArray<float>(m, "MjFloatVec");
+  DefineArray<int>(m, "MjIntVec");
 
   // ============================= MJSPEC =====================================
   mjSpec.def(py::init<>());

python/mujoco/specs_test.py

@@ -98,9 +98,13 @@ class SpecsTest(absltest.TestCase):
     site = body.add_site()
     site.name = 'sitename'
     site.type = mujoco.mjtGeom.mjGEOM_BOX
-    site.userdata = [1, 2, 3, 4, 5, 6]
+    site.userdata = [7, 2, 3, 4, 5, 6]
     self.assertEqual(site.name, 'sitename')
     self.assertEqual(site.type, mujoco.mjtGeom.mjGEOM_BOX)
+    np.testing.assert_array_equal(site.userdata, [7, 2, 3, 4, 5, 6])
+
+    # Modify a single element of userdata.
+    site.userdata[0] = 1
     np.testing.assert_array_equal(site.userdata, [1, 2, 3, 4, 5, 6])
 
     # Compile the spec and check for expected values in the model.