make the dm_control dependency opt-in

Author: Razer

pyproject.toml

@@ -57,7 +57,6 @@ dependencies = [# Optional
     'transformations',
     'absl-py',
     'lxml',
-    'dm_control',
     'pyyaml'
 ]
 
@@ -71,6 +70,7 @@ dependencies = [# Optional
 # projects.
 [project.optional-dependencies] # Optional
 test = ["pytest"]
+mujoco = ["dm_control"]
 
 # List URLs that are relevant to your project
 #
@@ -102,4 +102,4 @@ test = ["pytest"]
 # These are the assumed default build requirements from pip:
 # https://pip.pypa.io/en/stable/reference/pip/#pep-517-and-518-support
 requires = ["setuptools>=43.0.0", "wheel"]
-build-backend = "setuptools.build_meta"
+build-backend = "setuptools.build_meta"

src/pytorch_kinematics/mjcf.py

@@ -1,5 +1,3 @@
-from dm_control import mjcf
-
 import pytorch_kinematics.transforms as tf
 from . import chain
 from . import frame
@@ -59,6 +57,8 @@ def build_chain_from_mjcf(data):
     chain.Chain
         Chain object created from MJCF.
     """
+    from dm_control import mjcf
+
     model = mjcf.from_xml_string(data)
     root_body = model.worldbody.body[0]
     root_frame = frame.Frame(root_body.name + "_frame",