Add plugin support to Python bindings.

PiperOrigin-RevId: 480675078
Change-Id: I2967654b6662efced8ae62cae9b03c6c8e65c67c

python/mujoco/__init__.py

@@ -54,5 +54,15 @@ if _MUJOCO_GL not in ('disable', 'disabled', 'off', 'false', '0'):
     from mujoco.glfw import GLContext
 
 HEADERS_DIR = os.path.join(os.path.dirname(__file__), 'include/mujoco')
+PLUGINS_DIR = os.path.join(os.path.dirname(__file__), 'plugin')
+
+PLUGIN_HANDLES = []
+
+def _load_all_bundled_plugins():
+  for directory, _, filenames in os.walk(PLUGINS_DIR):
+    for filename in filenames:
+      PLUGIN_HANDLES.append(ctypes.CDLL(os.path.join(directory, filename)))
+
+_load_all_bundled_plugins()
 
 __version__ = mj_versionString()  # pylint: disable=undefined-variable

python/mujoco/bindings_test.py

@@ -69,6 +69,14 @@ TEST_XML_SENSOR = r"""
 </mujoco>
 """
 
+TEST_XML_PLUGIN = r"""
+<mujoco model="test">
+  <extension>
+    <required plugin="mujoco.elasticity.cable"/>
+  </extension>
+</mujoco>
+"""
+
 
 @contextlib.contextmanager
 def temporary_callback(setter, callback):
@@ -1111,5 +1119,8 @@ Euler integrator, semi-implicit in velocity.
         self.fail("Attribute '{}' differs from expected value: {}".format(
             name, str(e)))
 
+  def test_load_plugin(self):
+    mujoco.MjModel.from_xml_string(TEST_XML_PLUGIN)
+
 if __name__ == '__main__':
   absltest.main()