Passing non asset arguments to InteractiveSceneCfg

[abhinavj98]

Hi all,

I'm trying to dynamically generate scenes by passing arguments like num_objects to a custom InteractiveSceneCfg and using them in __post_init__ to create the assets.

However, the InteractiveScene parser throws a ValueError because it incorrectly tries to spawn my helper variable as a scene asset.

Example Code:

from isaaclab.utils.configclass import configclass
from isaaclab.scene import InteractiveScene, InteractiveSceneCfg

@configclass
class MyDynamicSceneCfg(InteractiveSceneCfg):
    # This helper variable causes the error
    num_objects: int = 10

    def __post_init__(self):
        super().__post_init__()
        # Logic to generate `num_objects` assets would go here...
        pass

Is this the wrong way to use the configclass? A suggestion would be to have a meta_data variable that gets ignored by the InteractiveScene parser.

[RandomOakForest]

Thank you for posting this. The issue you're facing—where adding a helper variable like num_objects to your InteractiveSceneCfg causes a ValueError from the InteractiveScene parser—is due to how Isaac Lab's InteractiveScene and configclass system expect configuration classes to operate. Every field in your configclass, unless handled specially, is interpreted as an asset or entity to instantiate in the scene. This is by design so that all configuration data relevant for scene instantiation is exposed and serializable, supporting vectorization and easy Hydra/CLI overrides.¹²³

Why the Error Occurs

• When you add num_objects: int to your scene config, the parser walks through each attribute of the configuration class and expects them to be asset configuration objects (subclasses of AssetBaseCfg, ArticulationCfg, TerrainImporterCfg, etc.) or scene attributes it understands (num_envs, env_spacing, etc.).
• If it encounters an attribute type/int that isn’t an asset—or built-in attribute—it tries to instantiate it as an asset, which fails and throws a ValueError.²³

Possible Workarounds

1. Use “meta_data” or "_helper" Prefix and Skip Logic

There isn’t an officially documented, built-in meta_data or helper attribute in the latest Isaac Lab. Instead, what you can do is:

• Use a naming convention (such as prefixing these helper/non-asset attributes with an underscore or placing them into a meta_data dictionary attribute).
• In your __post_init__, process these values as needed, but the InteractiveScene parser will still visit these attributes unless you remove them before super().post_init(), or they are not type-annotated as fields.

2. Storing Helper Data in a Dict/Property (Recommended)

The best-documented pattern is to avoid adding plain ints/floats/lists as typed fields on your InteractiveSceneCfg. Instead:

• Store helper values as a property method or in a class variable not marked as a configclass dataclass field.
• Use them in __post_init__ logic, but don’t assign them as annotated config fields.

3. Only Use Annotated Fields for Scene Entities

Review the official [scene creation tutorial] and API docs: every field of the configclass scene config should be a scene entity or a proper config setting (num_envs, env_spacing, etc.). Helper variables should not be fields.³²

Example: Safe Pattern

from isaaclab.utils.configclass import configclass
from isaaclab.scene import InteractiveScene, InteractiveSceneCfg

@configclass
class MyDynamicSceneCfg(InteractiveSceneCfg):
    # Only config fields for actual scene assets/entities!
    pass

def make_dynamic_scene_cfg(num_objects):
    cfg = MyDynamicSceneCfg()
    # Now, in __post_init__ or after construction, use num_objects to mutate cfg
    # Or append objects programmatically here instead of declaring num_objects as a field
    for i in range(num_objects):
        # Dynamically add assets with unique names
        setattr(cfg, f"dyn_asset_{i}", ...config for asset...)
    return cfg

Or, if you want to store meta info:

@configclass
class MyDynamicSceneCfg(InteractiveSceneCfg):
    # Only scene assets/entities here

    def __post_init__(self):
        super().__post_init__()
        self._meta_data = {"num_objects": 10}
        # Use self._meta_data['num_objects'] internally, but do not declare as field

Footnotes

1. https://isaac-sim.github.io/IsaacLab/main/source/api/lab/isaaclab.terrains.html ↩

2. https://isaac-sim.github.io/IsaacLab/main/source/api/lab/isaaclab.scene.html ↩ ↩² ↩³

3. https://isaac-sim.github.io/IsaacLab/main/source/tutorials/02_scene/create_scene.html ↩ ↩² ↩³