Lazifies IsaacLab import system

source/isaaclab/config/extension.toml

@@ -1,7 +1,7 @@
 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "4.2.1"
+version = "4.4.0"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"
@@ -16,6 +16,7 @@ requirements = [
     "numpy",
     "prettytable==3.3.0",
     "toml",
+    "lazy_loader>=0.4",
     "hidapi",
     "gymnasium==0.29.0",
     "trimesh",
@@ -26,6 +27,7 @@ modules = [
     "numpy",
     "prettytable",
     "toml",
+    "lazy_loader",
     "hid",
     "gymnasium",
     "trimesh",

source/isaaclab/docs/CHANGELOG.rst

@@ -1,6 +1,36 @@
 Changelog
 ---------
 
+4.4.0 (2026-02-26)
+~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* Refined lazy-loading behavior for config-only import paths to keep environment
+  config construction backend-free. This includes stricter cascading namespace
+  resolution in :func:`~isaaclab.utils.module.attach_cascading`, avoiding eager
+  callable resolution during deepcopy of :class:`~isaaclab.utils.string.ResolvableString`,
+  and updating locomanipulation MDP exports/import boundaries so
+  ``test_env_cfg_no_forbidden_imports.py`` passes without importing runtime modules.
+
+
+4.3.0 (2026-02-26)
+~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* Added lazy callable-string resolution for config fields through
+  :class:`~isaaclab.utils.string.ResolvableString` in :mod:`isaaclab.utils.configclass`.
+  Config values such as ``class_type``/``func`` can now remain as strings until first
+  use and then resolve/cached automatically.
+
+* Added ``{DIR}`` callable-string shorthand support in :mod:`isaaclab.utils.configclass`
+  for config defaults. ``"{DIR}.module:Symbol"`` now expands to the declaring config
+  module directory before resolution.
+
+
 4.2.1 (2026-02-25)
 ~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/actuators/__init__.py

@@ -22,15 +22,19 @@
 and called by the :class:`isaaclab.assets.Articulation` class.
 """
 
-from .actuator_base import ActuatorBase
-from .actuator_base_cfg import ActuatorBaseCfg
-from .actuator_net import ActuatorNetLSTM, ActuatorNetMLP
-from .actuator_net_cfg import ActuatorNetLSTMCfg, ActuatorNetMLPCfg
-from .actuator_pd import DCMotor, DelayedPDActuator, IdealPDActuator, ImplicitActuator, RemotizedPDActuator
-from .actuator_pd_cfg import (
-    DCMotorCfg,
-    DelayedPDActuatorCfg,
-    IdealPDActuatorCfg,
-    ImplicitActuatorCfg,
-    RemotizedPDActuatorCfg,
+from isaaclab.utils.lazy_imports import lazy_export
+
+lazy_export(
+    ("actuator_base", "ActuatorBase"),
+    ("actuator_base_cfg", "ActuatorBaseCfg"),
+    ("actuator_net", ["ActuatorNetLSTM", "ActuatorNetMLP"]),
+    ("actuator_net_cfg", ["ActuatorNetLSTMCfg", "ActuatorNetMLPCfg"]),
+    ("actuator_pd", ["DCMotor", "DelayedPDActuator", "IdealPDActuator", "ImplicitActuator", "RemotizedPDActuator"]),
+    ("actuator_pd_cfg", [
+        "DCMotorCfg",
+        "DelayedPDActuatorCfg",
+        "IdealPDActuatorCfg",
+        "ImplicitActuatorCfg",
+        "RemotizedPDActuatorCfg",
+    ]),
 )

source/isaaclab/isaaclab/actuators/actuator_net_cfg.py

@@ -5,19 +5,21 @@
 
 from collections.abc import Iterable
 from dataclasses import MISSING
-from typing import Literal
+from typing import TYPE_CHECKING, Literal
 
 from isaaclab.utils import configclass
 
-from . import actuator_net
 from .actuator_pd_cfg import DCMotorCfg
 
+if TYPE_CHECKING:
+    from .actuator_net import ActuatorNetLSTM, ActuatorNetMLP
+
 
 @configclass
 class ActuatorNetLSTMCfg(DCMotorCfg):
     """Configuration for LSTM-based actuator model."""
 
-    class_type: type = actuator_net.ActuatorNetLSTM
+    class_type: type["ActuatorNetLSTM"] | str = "{DIR}.actuator_net:ActuatorNetLSTM"
     # we don't use stiffness and damping for actuator net
     stiffness = None
     damping = None
@@ -30,7 +32,7 @@ class ActuatorNetLSTMCfg(DCMotorCfg):
 class ActuatorNetMLPCfg(DCMotorCfg):
     """Configuration for MLP-based actuator model."""
 
-    class_type: type = actuator_net.ActuatorNetMLP
+    class_type: type["ActuatorNetMLP"] | str = "{DIR}.actuator_net:ActuatorNetMLP"
     # we don't use stiffness and damping for actuator net
 
     stiffness = None

source/isaaclab/isaaclab/actuators/actuator_pd_cfg.py

@@ -4,12 +4,15 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 from dataclasses import MISSING
+from typing import TYPE_CHECKING
 
 from isaaclab.utils import configclass
 
-from . import actuator_pd
 from .actuator_base_cfg import ActuatorBaseCfg
 
+if TYPE_CHECKING:
+    from .actuator_pd import DCMotor, DelayedPDActuator, IdealPDActuator, ImplicitActuator, RemotizedPDActuator
+
 """
 Implicit Actuator Models.
 """
@@ -23,7 +26,7 @@ class ImplicitActuatorCfg(ActuatorBaseCfg):
         The PD control is handled implicitly by the simulation.
     """
 
-    class_type: type = actuator_pd.ImplicitActuator
+    class_type: type["ImplicitActuator"] | str = "{DIR}.actuator_pd:ImplicitActuator"
 
 
 """
@@ -35,14 +38,14 @@ class ImplicitActuatorCfg(ActuatorBaseCfg):
 class IdealPDActuatorCfg(ActuatorBaseCfg):
     """Configuration for an ideal PD actuator."""
 
-    class_type: type = actuator_pd.IdealPDActuator
+    class_type: type["IdealPDActuator"] | str = "{DIR}.actuator_pd:IdealPDActuator"
 
 
 @configclass
 class DCMotorCfg(IdealPDActuatorCfg):
     """Configuration for direct control (DC) motor actuator model."""
 
-    class_type: type = actuator_pd.DCMotor
+    class_type: type["DCMotor"] | str = "{DIR}.actuator_pd:DCMotor"
 
     saturation_effort: float = MISSING
     """Peak motor force/torque of the electric DC motor (in N-m)."""
@@ -52,7 +55,7 @@ class DCMotorCfg(IdealPDActuatorCfg):
 class DelayedPDActuatorCfg(IdealPDActuatorCfg):
     """Configuration for a delayed PD actuator."""
 
-    class_type: type = actuator_pd.DelayedPDActuator
+    class_type: type["DelayedPDActuator"] | str = "{DIR}.actuator_pd:DelayedPDActuator"
 
     min_delay: int = 0
     """Minimum number of physics time-steps with which the actuator command may be delayed. Defaults to 0."""
@@ -71,7 +74,7 @@ class RemotizedPDActuatorCfg(DelayedPDActuatorCfg):
         the output torques.
     """
 
-    class_type: type = actuator_pd.RemotizedPDActuator
+    class_type: type["RemotizedPDActuator"] | str = "{DIR}.actuator_pd:RemotizedPDActuator"
 
     joint_parameter_lookup: list[list[float]] = MISSING
     """Joint parameter lookup table. Shape is (num_lookup_points, 3).

source/isaaclab/isaaclab/assets/__init__.py

@@ -38,28 +38,18 @@
 the corresponding actuator torques.
 """
 
-from .articulation import BaseArticulation, BaseArticulationData, Articulation, ArticulationCfg, ArticulationData
-from .asset_base import AssetBase
-from .asset_base_cfg import AssetBaseCfg
-from .rigid_object import BaseRigidObject, BaseRigidObjectData, RigidObject, RigidObjectCfg, RigidObjectData
-from .rigid_object_collection import BaseRigidObjectCollection, BaseRigidObjectCollectionData, RigidObjectCollection, RigidObjectCollectionCfg, RigidObjectCollectionData
-
-__all__ = [
-    "AssetBase",
-    "AssetBaseCfg",
-    "BaseArticulation",
-    "BaseArticulationData",
-    "Articulation",
-    "ArticulationCfg",
-    "ArticulationData",
-    "BaseRigidObject",
-    "BaseRigidObjectData",
-    "RigidObject",
-    "RigidObjectCfg",
-    "RigidObjectData",
-    "BaseRigidObjectCollection",
-    "BaseRigidObjectCollectionData",
-    "RigidObjectCollection",
-    "RigidObjectCollectionCfg",
-    "RigidObjectCollectionData",
-]
+from isaaclab.utils.lazy_imports import lazy_export
+
+lazy_export(
+    ("asset_base", "AssetBase"),
+    ("asset_base_cfg", "AssetBaseCfg"),
+    ("articulation", ["BaseArticulation", "BaseArticulationData", "Articulation", "ArticulationCfg", "ArticulationData"]),
+    ("rigid_object", ["BaseRigidObject", "BaseRigidObjectData", "RigidObject", "RigidObjectCfg", "RigidObjectData"]),
+    ("rigid_object_collection", [
+        "BaseRigidObjectCollection",
+        "BaseRigidObjectCollectionData",
+        "RigidObjectCollection",
+        "RigidObjectCollectionCfg",
+        "RigidObjectCollectionData",
+    ]),
+)

source/isaaclab/isaaclab/assets/articulation/__init__.py

@@ -5,16 +5,12 @@
 
 """Sub-module for rigid articulated assets."""
 
-from .base_articulation import BaseArticulation
-from .base_articulation_data import BaseArticulationData
-from .articulation import Articulation
-from .articulation_cfg import ArticulationCfg
-from .articulation_data import ArticulationData
+from isaaclab.utils.lazy_imports import lazy_export
 
-__all__ = [
-    "BaseArticulation",
-    "BaseArticulationData",
-    "Articulation",
-    "ArticulationCfg",
-    "ArticulationData",
-]
+lazy_export(
+    ("base_articulation", "BaseArticulation"),
+    ("base_articulation_data", "BaseArticulationData"),
+    ("articulation", "Articulation"),
+    ("articulation_cfg", "ArticulationCfg"),
+    ("articulation_data", "ArticulationData"),
+)

source/isaaclab/isaaclab/assets/articulation/articulation_cfg.py

@@ -6,12 +6,15 @@
 from __future__ import annotations
 
 from dataclasses import MISSING
+from typing import TYPE_CHECKING
 
 from isaaclab.actuators import ActuatorBaseCfg
 from isaaclab.utils import configclass
 
 from ..asset_base_cfg import AssetBaseCfg
-from .articulation import Articulation
+
+if TYPE_CHECKING:
+    from .articulation import Articulation
 
 
 @configclass
@@ -38,7 +41,7 @@ class InitialStateCfg(AssetBaseCfg.InitialStateCfg):
     # Initialize configurations.
     ##
 
-    class_type: type = Articulation
+    class_type: type[Articulation] | str = "{DIR}.articulation:Articulation"
 
     articulation_root_prim_path: str | None = None
     """Path to the articulation root prim under the :attr:`prim_path`. Defaults to None, in which case the class

source/isaaclab/isaaclab/assets/asset_base.py

@@ -15,7 +15,7 @@
 import torch
 
 import isaaclab.sim as sim_utils
-from isaaclab.physics import PhysicsEvent, PhysicsManager
+from isaaclab.physics import PhysicsEvent
 from isaaclab.sim.simulation_context import SimulationContext
 from isaaclab.sim.utils.stage import get_current_stage
 
@@ -310,8 +310,8 @@ def _initialize_callback(self, event):
             :attr:`PhysicsEvent.PHYSICS_READY` is dispatched by the current backend.
         """
         if not self._is_initialized:
-            self._backend = PhysicsManager.get_backend()
-            self._device = PhysicsManager.get_device()
+            self._backend = SimulationContext.instance().physics_manager.get_backend()
+            self._device = SimulationContext.instance().physics_manager.get_device()
             try:
                 self._initialize_impl()
             except Exception as e:

source/isaaclab/isaaclab/assets/asset_base_cfg.py

@@ -11,8 +11,6 @@
 from isaaclab.sim import SpawnerCfg
 from isaaclab.utils import configclass
 
-from .asset_base import AssetBase
-
 
 @configclass
 class AssetBaseCfg:
@@ -41,7 +39,7 @@ class InitialStateCfg:
         Defaults to (0.0, 0.0, 0.0, 1.0).
         """
 
-    class_type: type[AssetBase] = None
+    class_type: type | str | None = None
     """The associated asset class. Defaults to None, which means that the asset will be spawned
     but cannot be interacted with via the asset class.
 

source/isaaclab/isaaclab/assets/rigid_object/__init__.py

@@ -5,16 +5,12 @@
 
 """Sub-module for rigid object assets."""
 
-from .base_rigid_object import BaseRigidObject
-from .base_rigid_object_data import BaseRigidObjectData
-from .rigid_object import RigidObject
-from .rigid_object_cfg import RigidObjectCfg
-from .rigid_object_data import RigidObjectData
+from isaaclab.utils.lazy_imports import lazy_export
 
-__all__ = [
-    "BaseRigidObject",
-    "BaseRigidObjectData",
-    "RigidObject",
-    "RigidObjectCfg",
-    "RigidObjectData",
-]
+lazy_export(
+    ("base_rigid_object", "BaseRigidObject"),
+    ("base_rigid_object_data", "BaseRigidObjectData"),
+    ("rigid_object", "RigidObject"),
+    ("rigid_object_cfg", "RigidObjectCfg"),
+    ("rigid_object_data", "RigidObjectData"),
+)

source/isaaclab/isaaclab/assets/rigid_object/rigid_object_cfg.py

@@ -3,10 +3,14 @@
 #
 # SPDX-License-Identifier: BSD-3-Clause
 
+from typing import TYPE_CHECKING
+
 from isaaclab.utils import configclass
 
 from ..asset_base_cfg import AssetBaseCfg
-from .rigid_object import RigidObject
+
+if TYPE_CHECKING:
+    from .rigid_object import RigidObject
 
 
 @configclass
@@ -26,7 +30,7 @@ class InitialStateCfg(AssetBaseCfg.InitialStateCfg):
     # Initialize configurations.
     ##
 
-    class_type: type = RigidObject
+    class_type: type["RigidObject"] | str = "{DIR}.rigid_object:RigidObject"
 
     init_state: InitialStateCfg = InitialStateCfg()
     """Initial state of the rigid object. Defaults to identity pose with zero velocity."""

source/isaaclab/isaaclab/assets/rigid_object_collection/__init__.py

@@ -5,16 +5,12 @@
 
 """Sub-module for rigid object collection."""
 
-from .base_rigid_object_collection import BaseRigidObjectCollection
-from .base_rigid_object_collection_data import BaseRigidObjectCollectionData
-from .rigid_object_collection import RigidObjectCollection
-from .rigid_object_collection_cfg import RigidObjectCollectionCfg
-from .rigid_object_collection_data import RigidObjectCollectionData
+from isaaclab.utils.lazy_imports import lazy_export
 
-__all__ = [
-    "BaseRigidObjectCollection",
-    "BaseRigidObjectCollectionData",
-    "RigidObjectCollection",
-    "RigidObjectCollectionCfg",
-    "RigidObjectCollectionData",
-]
+lazy_export(
+    ("base_rigid_object_collection", "BaseRigidObjectCollection"),
+    ("base_rigid_object_collection_data", "BaseRigidObjectCollectionData"),
+    ("rigid_object_collection", "RigidObjectCollection"),
+    ("rigid_object_collection_cfg", "RigidObjectCollectionCfg"),
+    ("rigid_object_collection_data", "RigidObjectCollectionData"),
+)