Allow keyword arguments in attach.

PiperOrigin-RevId: 702718597
Change-Id: I1f1a5e9c88c8e102d5cbe5984511e7923ec7be3e

python/mujoco/specs.cc

@@ -625,15 +625,19 @@ PYBIND11_MODULE(_specs, m) {
       py::return_value_policy::reference_internal);
   mjsBody.def(
       "attach_frame",
-      [](raw::MjsBody& self, raw::MjsFrame& frame, std::string& prefix,
+      [](raw::MjsBody& self, raw::MjsFrame& frame,
-         std::string& suffix) -> raw::MjsFrame* {
+         std::optional<std::string>& prefix,
-        auto new_frame =
+         std::optional<std::string>& suffix) -> raw::MjsFrame* {
-            mjs_attachFrame(&self, &frame, prefix.c_str(), suffix.c_str());
+        const char* p = prefix.has_value() ? prefix.value().c_str() : "";
+        const char* s = suffix.has_value() ? suffix.value().c_str() : "";
+        auto new_frame = mjs_attachFrame(&self, &frame, p, s);
         if (!new_frame) {
           throw pybind11::value_error(mjs_getError(mjs_getSpec(self.element)));
         }
         return new_frame;
       },
+      py::arg("frame"), py::arg("prefix") = py::none(),
+      py::arg("suffix") = py::none(),
       py::return_value_policy::reference_internal);
   mjsBody.def(
     "to_frame",
@@ -654,34 +658,41 @@ PYBIND11_MODULE(_specs, m) {
   });
   mjsFrame.def(
       "attach_body",
-      [](raw::MjsFrame& self, raw::MjsBody& body, std::string& prefix,
+      [](raw::MjsFrame& self, raw::MjsBody& body,
-         std::string& suffix) -> raw::MjsBody* {
+         std::optional<std::string>& prefix,
-        auto new_body =
+         std::optional<std::string>& suffix) -> raw::MjsBody* {
-            mjs_attachBody(&self, &body, prefix.c_str(), suffix.c_str());
+        const char* p = prefix.has_value() ? prefix.value().c_str() : "";
+        const char* s = suffix.has_value() ? suffix.value().c_str() : "";
+        auto new_body = mjs_attachBody(&self, &body, p, s);
         if (!new_body) {
           throw pybind11::value_error(
               mjs_getError(mjs_getSpec(self.element)));
         }
         return new_body;
       },
+      py::arg("body"), py::arg("prefix") = py::none(),
+      py::arg("suffix") = py::none(),
       py::return_value_policy::reference_internal);
   mjsFrame.def(
       "attach",
-      [](raw::MjsFrame& self, MjSpec& spec, std::string& prefix,
+      [](raw::MjsFrame& self, MjSpec& spec, std::optional<std::string>& prefix,
-         std::string& suffix) -> raw::MjsFrame* {
+         std::optional<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 =
+        const char* p = prefix.has_value() ? prefix.value().c_str() : "";
-            mjs_attachBody(&self, world, prefix.c_str(), suffix.c_str());
+        const char* s = suffix.has_value() ? suffix.value().c_str() : "";
+        auto attached_world = mjs_attachBody(&self, world, p, s);
         if (!attached_world) {
           throw pybind11::value_error(
               mjs_getError(mjs_getSpec(self.element)));
         }
         return mjs_bodyToFrame(&attached_world);
       },
+      py::arg("spec"), py::arg("prefix") = py::none(),
+      py::arg("suffix") = py::none(),
       py::return_value_policy::reference_internal);
 
   // ============================= MJSGEOM =====================================
@@ -730,16 +741,20 @@ PYBIND11_MODULE(_specs, m) {
       py::return_value_policy::reference_internal);
   mjsSite.def(
       "attach",
-      [](raw::MjsSite& self, raw::MjsBody& body, std::string& prefix,
+      [](raw::MjsSite& self, raw::MjsBody& body,
-         std::string& suffix) -> raw::MjsBody* {
+         std::optional<std::string>& prefix,
-        auto new_body =
+         std::optional<std::string>& suffix) -> raw::MjsBody* {
-            mjs_attachToSite(&self, &body, prefix.c_str(), suffix.c_str());
+        const char* p = prefix.has_value() ? prefix.value().c_str() : "";
+        const char* s = suffix.has_value() ? suffix.value().c_str() : "";
+        auto new_body = mjs_attachToSite(&self, &body, p, s);
         if (!new_body) {
           throw pybind11::value_error(
               mjs_getError(mjs_getSpec(self.element)));
         }
         return new_body;
       },
+      py::arg("body"), py::arg("prefix") = py::none(),
+      py::arg("suffix") = py::none(),
       py::return_value_policy::reference_internal);
 
   // ============================= MJSCAMERA ===================================

python/mujoco/specs_test.py

@@ -867,7 +867,7 @@ class SpecsTest(absltest.TestCase):
     parent.compiler.degree = not child.compiler.degree
     body = child.worldbody.add_body(euler=[90, 0, 0])
     frame = parent.worldbody.add_frame(euler=[-mujoco.mjPI / 2, 0, 0])
-    frame.attach_body(body, 'child-', '')
+    frame.attach_body(body, prefix='child-')
     model = parent.compile()
     np.testing.assert_almost_equal(model.body_quat[1], [1, 0, 0, 0])
 
@@ -876,7 +876,7 @@ class SpecsTest(absltest.TestCase):
     parent = mujoco.MjSpec()
     site = parent.worldbody.add_site(pos=[1, 2, 3])
     body = child.worldbody.add_body()
-    self.assertIsNotNone(site.attach(body, '_', ''))
+    self.assertIsNotNone(site.attach(body, prefix='_'))
     model = parent.compile()
     np.testing.assert_array_equal(model.body_pos[1], [1, 2, 3])
 
@@ -892,7 +892,7 @@ class SpecsTest(absltest.TestCase):
     child.worldbody.add_camera(name='camera')
     parent = mujoco.MjSpec()
     frame = parent.worldbody.add_frame(name='frame')
-    frame.attach(child, 'child-', '')
+    frame.attach(child, prefix='child-')
     self.assertLen(child.cameras, 1)
     self.assertLen(parent.bodies, 1)
     self.assertLen(parent.frames, 2)