Enable to attach a spec to a frame.

PiperOrigin-RevId: 699703988
Change-Id: Idbddcbce1e68286248458eb0bd24d5080451a58a

python/mujoco/specs.cc

@@ -665,6 +665,24 @@ PYBIND11_MODULE(_specs, m) {
         return new_body;
       },
       py::return_value_policy::reference_internal);
+  mjsFrame.def(
+      "attach",
+      [](raw::MjsFrame& self, MjSpec& spec, std::string& prefix,
+         std::string& suffix) -> raw::MjsFrame* {
+        auto world = mjs_findBody(spec.ptr, "world");
+        if (!world) {
+          throw pybind11::value_error(
+              mjs_getError(mjs_getSpec(self.element)));
+        }
+        auto attached_world =
+            mjs_attachBody(&self, world, prefix.c_str(), suffix.c_str());
+        if (!attached_world) {
+          throw pybind11::value_error(
+              mjs_getError(mjs_getSpec(self.element)));
+        }
+        return mjs_bodyToFrame(&attached_world);
+      },
+      py::return_value_policy::reference_internal);
 
   // ============================= MJSGEOM =====================================
   mjsGeom.def("delete", [](raw::MjsGeom& self) { mjs_delete(self.element); });

python/mujoco/specs_test.py

@@ -884,6 +884,19 @@ class SpecsTest(absltest.TestCase):
     frame = body.to_frame()
     np.testing.assert_array_equal(frame.pos, [1, 2, 3])
 
+  def test_attach_spec_to_frame(self):
+    child = mujoco.MjSpec()
+    child.worldbody.add_camera(name='camera')
+    parent = mujoco.MjSpec()
+    frame = parent.worldbody.add_frame(name='frame')
+    frame.attach(child, 'child-', '')
+    self.assertLen(child.cameras, 1)
+    self.assertLen(parent.bodies, 1)
+    self.assertLen(parent.frames, 2)
+    self.assertEqual(parent.cameras[0].name, 'child-camera')
+    self.assertEqual(parent.frames[0].name, 'frame')
+    self.assertEqual(parent.frames[1].name, '')
+
 
 if __name__ == '__main__':
   absltest.main()