Change MjSpec.default from method to attribute.

PiperOrigin-RevId: 730912407
Change-Id: I0147acbd257ecc8b72752a2992a7d4ea6e1b4c07

Author: quagla

python/mujoco/specs.cc

@@ -474,7 +474,7 @@ PYBIND11_MODULE(_specs, m) {
         return mjs_addDefault(spec->ptr, classname.c_str(), parent);
       },
       py::return_value_policy::reference_internal);
-  mjSpec.def(
+  mjSpec.def_property_readonly(
       "default",
       [](MjSpec& self) -> raw::MjsDefault* {
         return mjs_getSpecDefault(self.ptr);

python/mujoco/specs_test.py

@@ -549,7 +549,7 @@ def test_modelname_default_class(self):
     spec = mujoco.MjSpec()
     spec.modelname = 'test'
 
-    main = spec.default()
+    main = spec.default
     main.geom.size[0] = 2
 
     def1 = spec.add_default('def1', main)
@@ -563,7 +563,7 @@ def test_modelname_default_class(self):
     spec = mujoco.MjSpec()
     spec.modelname = 'test'
 
-    main = spec.default()
+    main = spec.default
     main.geom.size[0] = 2
     def1 = spec.add_default('def1', main)
     def1.geom.size[0] = 3
@@ -579,7 +579,7 @@ def test_modelname_default_class(self):
     spec = mujoco.MjSpec()
     spec.modelname = 'test'
 
-    main = spec.default()
+    main = spec.default
     main.geom.size[0] = 2
     def1 = spec.add_default('def1', main)
     def1.geom.size[0] = 3