Make "id" a property rather than a method of mjsElements in Python bindings.

PiperOrigin-RevId: 649424035
Change-Id: I8226b3040aa2001ae9748399257e36ac263b7c8b

python/mujoco/specs.cc

@@ -13,21 +13,21 @@
 // limitations under the License.
 
 #include <array>
-#include <cstddef>
+#include <cstddef>  // IWYU pragma: keep
 #include <cstdint>
 #include <memory>
 #include <string>
-#include <string_view>
+#include <string_view>  // IWYU pragma: keep
-#include <vector>
+#include <vector>  // IWYU pragma: keep
 
 #include <Eigen/Core>
 #include <Eigen/Eigen>
-#include <mujoco/mjspec.h>
+#include <mujoco/mjspec.h>  // IWYU pragma: keep
 #include <mujoco/mujoco.h>
 #include "errors.h"
-#include "indexers.h"
+#include "indexers.h"  // IWYU pragma: keep
 #include "raw.h"
-#include "structs.h"
+#include "structs.h"  // IWYU pragma: keep
 #include <pybind11/cast.h>
 #include <pybind11/eigen.h>
 #include <pybind11/eigen/matrix.h>
@@ -490,10 +490,10 @@ PYBIND11_MODULE(_specs, m) {
     },
     py::return_value_policy::reference_internal);
 
-  // ============================= MJSBODY ====================================
+  // ============================= MJSBODY =====================================
-  mjsBody.def("id", [](raw::MjsBody& self) -> int {
+  mjsBody.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsBody& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsBody.def("delete", [](raw::MjsBody& self) { mjs_delete(self.element); });
   mjsBody.def(
       "add_body",
@@ -665,9 +665,9 @@ PYBIND11_MODULE(_specs, m) {
               });
 
   // ============================= MJSFRAME ====================================
-  mjsFrame.def("id", [](raw::MjsFrame& self) -> int {
+  mjsFrame.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsFrame& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsFrame.def("delete", [](raw::MjsFrame& self) { mjs_delete(self.element); });
   mjsFrame.def("set_frame", [](raw::MjsFrame& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
@@ -677,10 +677,10 @@ PYBIND11_MODULE(_specs, m) {
     mjs_attachBody(&self, &body, prefix.c_str(), suffix.c_str());
   });
 
-  // ============================= MJSGEOM ====================================
+  // ============================= MJSGEOM =====================================
-  mjsGeom.def("id", [](raw::MjsGeom& self) -> int {
+  mjsGeom.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsGeom& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsGeom.def("delete", [](raw::MjsGeom& self) { mjs_delete(self.element); });
   mjsGeom.def("set_frame", [](raw::MjsGeom& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
@@ -696,9 +696,9 @@ PYBIND11_MODULE(_specs, m) {
       py::return_value_policy::reference_internal);
 
   // ============================= MJSJOINT ====================================
-  mjsJoint.def("id", [](raw::MjsJoint& self) -> int {
+  mjsJoint.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsJoint& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsJoint.def("delete", [](raw::MjsJoint& self) { mjs_delete(self.element); });
   mjsJoint.def("set_frame", [](raw::MjsJoint& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
@@ -713,10 +713,10 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSSITE ====================================
+  // ============================= MJSSITE =====================================
-  mjsSite.def("id", [](raw::MjsSite& self) -> int {
+  mjsSite.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsSite& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsSite.def("delete", [](raw::MjsSite& self) { mjs_delete(self.element); });
   mjsSite.def("set_frame", [](raw::MjsSite& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
@@ -731,10 +731,10 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSCAMERA ==================================
+  // ============================= MJSCAMERA ===================================
-  mjsCamera.def("id", [](raw::MjsCamera& self) -> int {
+  mjsCamera.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsCamera& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsCamera.def("delete",
                 [](raw::MjsCamera& self) { mjs_delete(self.element); });
   mjsCamera.def("set_frame", [](raw::MjsCamera& self, raw::MjsFrame& frame) {
@@ -751,9 +751,9 @@ PYBIND11_MODULE(_specs, m) {
       py::return_value_policy::reference_internal);
 
   // ============================= MJSLIGHT ====================================
-  mjsLight.def("id", [](raw::MjsLight& self) -> int {
+  mjsLight.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsLight& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsLight.def("delete", [](raw::MjsLight& self) { mjs_delete(self.element); });
   mjsLight.def("set_frame", [](raw::MjsLight& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
@@ -768,10 +768,11 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSMATERIAL ================================
+  // ============================= MJSMATERIAL =================================
-  mjsMaterial.def("id", [](raw::MjsMaterial& self) -> int {
+  mjsMaterial.def_property_readonly(
-    return mjs_getId(self.element);
+      "id",
-  });
+      [](raw::MjsMaterial& self) -> int { return mjs_getId(self.element); },
+      py::return_value_policy::reference_internal);
   mjsMaterial.def("delete",
                   [](raw::MjsMaterial& self) { mjs_delete(self.element); });
   mjsMaterial.def("set_default",
@@ -785,10 +786,10 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSMESH ====================================
+  // ============================= MJSMESH =====================================
-  mjsMesh.def("id", [](raw::MjsMesh& self) -> int {
+  mjsMesh.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsMesh& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsMesh.def("delete", [](raw::MjsMesh& self) { mjs_delete(self.element); });
   mjsMesh.def("set_default", [](raw::MjsMesh& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
@@ -800,10 +801,10 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSPAIR ====================================
+  // ============================= MJSPAIR =====================================
-  mjsPair.def("id", [](raw::MjsPair& self) -> int {
+  mjsPair.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsPair& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsPair.def("delete", [](raw::MjsPair& self) { mjs_delete(self.element); });
   mjsPair.def("set_default", [](raw::MjsPair& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
@@ -816,9 +817,10 @@ PYBIND11_MODULE(_specs, m) {
       py::return_value_policy::reference_internal);
 
   // ============================= MJSEQUAL ====================================
-  mjsEquality.def("id", [](raw::MjsEquality& self) -> int {
+  mjsEquality.def_property_readonly(
-    return mjs_getId(self.element);
+      "id",
-  });
+      [](raw::MjsEquality& self) -> int { return mjs_getId(self.element); },
+      py::return_value_policy::reference_internal);
   mjsEquality.def("delete",
                   [](raw::MjsEquality& self) { mjs_delete(self.element); });
   mjsEquality.def("set_default",
@@ -832,10 +834,11 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSACTUATOR ================================
+  // ============================= MJSACTUATOR =================================
-  mjsActuator.def("id", [](raw::MjsActuator& self) -> int {
+  mjsActuator.def_property_readonly(
-    return mjs_getId(self.element);
+      "id",
-  });
+      [](raw::MjsActuator& self) -> int { return mjs_getId(self.element); },
+      py::return_value_policy::reference_internal);
   mjsActuator.def("delete",
                   [](raw::MjsActuator& self) { mjs_delete(self.element); });
   mjsActuator.def("set_default",
@@ -849,10 +852,10 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSTENDON ==================================
+  // ============================= MJSTENDON ===================================
-  mjsTendon.def("id", [](raw::MjsTendon& self) -> int {
+  mjsTendon.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsTendon& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsTendon.def("delete",
                 [](raw::MjsTendon& self) { mjs_delete(self.element); });
   mjsTendon.def("set_default", [](raw::MjsTendon& self, raw::MjsDefault& def) {
@@ -889,71 +892,72 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::return_value_policy::reference_internal);
 
-  // ============================= MJSSENSOR ==================================
+  // ============================= MJSSENSOR ===================================
-  mjsSensor.def("id", [](raw::MjsSensor& self) -> int {
+  mjsSensor.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsSensor& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsSensor.def("delete",
                 [](raw::MjsSensor& self) { mjs_delete(self.element); });
 
-  // ============================= MJSFLEX ====================================
+  // ============================= MJSFLEX =====================================
-  mjsFlex.def("id", [](raw::MjsFlex& self) -> int {
+  mjsFlex.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsFlex& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsFlex.def("delete", [](raw::MjsFlex& self) { mjs_delete(self.element); });
 
-  // ============================= MJSHFIELD ==================================
+  // ============================= MJSHFIELD ===================================
-  mjsHField.def("id", [](raw::MjsHField& self) -> int {
+  mjsHField.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsHField& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsHField.def("delete",
                 [](raw::MjsHField& self) { mjs_delete(self.element); });
 
-  // ============================= MJSSKIN ====================================
+  // ============================= MJSSKIN =====================================
-  mjsSkin.def("id", [](raw::MjsSkin& self) -> int {
+  mjsSkin.def_property_readonly(
-    return mjs_getId(self.element);
+      "id", [](raw::MjsSkin& self) -> int { return mjs_getId(self.element); },
-  });
+      py::return_value_policy::reference_internal);
   mjsSkin.def("delete", [](raw::MjsSkin& self) { mjs_delete(self.element); });
 
-  // ============================= MJSTEXTURE =================================
+  // ============================= MJSTEXTURE ==================================
-  mjsTexture.def("id", [](raw::MjsTexture& self) -> int {
+  mjsTexture.def_property_readonly(
-    return mjs_getId(self.element);
+      "id",
-  });
+      [](raw::MjsTexture& self) -> int { return mjs_getId(self.element); },
+      py::return_value_policy::reference_internal);
   mjsTexture.def("delete",
                  [](raw::MjsTexture& self) { mjs_delete(self.element); });
 
-  // ============================= MJSKEY =====================================
+  // ============================= MJSKEY ======================================
   mjsKey.def("id",
              [](raw::MjsKey& self) -> int { return mjs_getId(self.element); });
   mjsKey.def("delete", [](raw::MjsKey& self) { mjs_delete(self.element); });
 
-  // ============================= MJSTEXT ====================================
+  // ============================= MJSTEXT =====================================
   mjsText.def("id", [](raw::MjsText& self) -> int {
     return mjs_getId(self.element);
   });
   mjsText.def("delete", [](raw::MjsText& self) { mjs_delete(self.element); });
 
-  // ============================= MJSNUMERIC =================================
+  // ============================= MJSNUMERIC ==================================
   mjsNumeric.def("id", [](raw::MjsNumeric& self) -> int {
     return mjs_getId(self.element);
   });
   mjsNumeric.def("delete",
                  [](raw::MjsNumeric& self) { mjs_delete(self.element); });
 
-  // ============================= MJSEXCLUDE ================================
+  // ============================= MJSEXCLUDE ==================================
   mjsExclude.def("id", [](raw::MjsExclude& self) -> int {
     return mjs_getId(self.element);
   });
   mjsExclude.def("delete",
                  [](raw::MjsExclude& self) { mjs_delete(self.element); });
 
-  // ============================= MJSTUPLE ===================================
+  // ============================= MJSTUPLE ====================================
   mjsTuple.def("id", [](raw::MjsTuple& self) -> int {
     return mjs_getId(self.element);
   });
   mjsTuple.def("delete", [](raw::MjsTuple& self) { mjs_delete(self.element); });
 
-  // ============================= MJSPLUGIN ==================================
+  // ============================= MJSPLUGIN ===================================
   mjsPlugin.def("id", [](raw::MjsPlugin& self) -> int {
     return mjs_getId(self.instance);
   });
@@ -961,6 +965,5 @@ PYBIND11_MODULE(_specs, m) {
                 [](raw::MjsPlugin& self) { mjs_delete(self.instance); });
 
 #include "specs.cc.inc"
-
 }  // PYBIND11_MODULE // NOLINT
 }  // namespace mujoco::python

python/mujoco/specs_test.py

@@ -66,13 +66,15 @@ class SpecsTest(absltest.TestCase):
     self.assertEqual(site.name, 'sitename')
     np.testing.assert_array_equal(site.userdata, [1, 2, 3, 4, 5, 6])
 
-    # Check that the site has no id before compilation.
+    # Check that the site and body have no id before compilation.
-    self.assertEqual(body.id(), -1)
+    self.assertEqual(body.id, -1)
+    self.assertEqual(site.id, -1)
 
     # Compile the spec and check for expected values in the model.
     model = spec.compile()
-    self.assertEqual(spec.worldbody.id(), 0)
+    self.assertEqual(spec.worldbody.id, 0)
-    self.assertEqual(body.id(), 1)
+    self.assertEqual(body.id, 1)
+    self.assertEqual(site.id, 0)
     self.assertEqual(model.nbody, 2)  # 2 bodies, including the world body
     np.testing.assert_array_equal(model.body_pos[1], [1, 2, 3])
     np.testing.assert_array_equal(model.body_quat[1], [0, 1, 0, 0])