mjxml 0.2.2

Utilities to programatically create MuJoCo XML configuration files

mjxml

Programmatic, type-checked helpers for composing MuJoCo XML. Define assets and worldbody elements in Python (with Pydantic validation), serialize to XML, and write files you can load in MuJoCo.

Highlights

• Strong typing and validation via Pydantic v2.
• Easy XML serialization: to_xml(), to_xml_str(), write().
• Assets: TextureAsset, MeshAsset, HFieldAsset, ModelAsset.
• Bodies: Geom (with many MuJoCo attributes), WorldBody base.
• Utilities: Defaults blocks, rotation helpers, and runtime type protocols.

Requirements

• Python >= 3.13
• Runtime deps: numpy, pydantic

Install

From PyPI:

pip install mjxml

Development

This project relies on uv. To setup a virtual environment, just do:

uv sync --dev
export PYTHONPATH=src

Quickstart

The snippets below sketch a typical flow: create assets, place them in the worldbody, and export a MuJoCo XML file.

1. Define assets with validation

from mjxml.asset.texture import TextureAsset
from mjxml.asset.mesh import MeshAsset

texture = TextureAsset(
    name="tex_grid",
    file="albedo.png",
    type="2d",
    colorspace="srgb",
    content_type="image/png",
    nchannel=3,
)

mesh = MeshAsset(
    name="m_cube",
    file="cube.obj",
    content_type="model/obj",
    scale=[1.0, 1.0, 1.0],
    inertia="exact",
)

Each asset only emits the attributes you set; Pydantic validators ensure parameters such as nchannel or scale stay within MuJoCo’s requirements.

2. Create bodies and geoms

from mjxml.body import Body, Geom

body = Body(name="torso")
body.add(
    Geom(
        name="box1",
        type="box",
        size=[0.5, 0.5, 0.5],
        material=None,
        rgba=[0.8, 0.2, 0.2, 1.0],
        friction=[0.5, 0.1, 0.01],
    )
)

Geoms automatically infer fields such as condim from the friction vector length and warn when MuJoCo would ignore an attribute.

3. Assemble a complete MujocoModel

from mjxml.model import MujocoModel

model = MujocoModel(name="demo")
model.add_asset(texture)
model.add_asset(mesh)
model.add_body(body)

root = model.to_xml()
print(model.to_xml_str())
model.write("scene.xml")

MujocoModel deduplicates identical assets, appends worldbody, actuator, and contact sections, and returns a ready-to-save ElementTree root.

Testing

Run the unit tests with pytest.

pytest -q -s

Status

This repository is under active development; expect minor API adjustments. A high-level MujocoModel aggregator is planned but not yet included.

Roadmap

• [✅] High-level Wrapper: MujocoModel class to aggregate assets, worldbody, and other sections.
• [✅] Body Elements: Support for joint, site, camera.
• [=] Sections: Support for actuator, sensor, equality, contact, tendon.
• [❌] IO: Parsing existing XML files for round-trip editing.
• [❌] Docs: Comprehensive API documentation and more examples.