API reference

MjSim: Basic simulation

mujoco_py.load_model_from_path(path)

Loads model from path.

mujoco_py.load_model_from_xml(xml_string)

Loads and returns a PyMjModel model from a string containing XML markup. Saves the XML string used to create the returned model in model.xml.

mujoco_py.load_model_from_mjb(path)

Loads and returns a PyMjModel model from bytes encoded MJB. MJB is a MuJoCo-custom format that includes assets like meshes/textures.

class mujoco_py.MjSim(model, data=None, nsubsteps=1, udd_callback=None)

MjSim represents a running simulation including its state.

Similar to Gym’s MujocoEnv, it internally wraps a PyMjModel and a PyMjData.

Parameters:

model : PyMjModel

The model to simulate.

data : PyMjData

Optional container for the simulation state. Will be created if None.

nsubsteps : int

Optional number of MuJoCo steps to run for every call to step(). Buffers will be swapped only once per step.

udd_callback : fn(MjSim) -> dict

Optional callback for user-defined dynamics. At every call to step(), it receives an MjSim object sim containing the current user-defined dynamics state in sim.udd_state, and returns the next udd_state after applying the user-defined dynamics. This is useful e.g. for reward functions that operate over functions of historical state.

Attributes

Methods

get_state()

Returns a copy of the simulator state.

render()

Renders view from a camera and returns image as an numpy.ndarray.

Args: - width (int): desired image width. - height (int): desired image height. - camera_name (str): name of camera in model. If None, the free

camera will be used.

• depth (bool): if True, also return depth buffer

Returns: - rgb (uint8 array): image buffer from camera - depth (float array): depth buffer from camera (only returned

if depth=True)

reset()

Resets the simulation data and clears buffers.

save()

Saves the simulator model and state to a file as either a MuJoCo XML or MJB file. The current state is saved as a keyframe in the model file. This is useful for debugging using MuJoCo’s simulate utility.

Note that this doesn’t save the UDD-state which is part of MjSimState, since that’s not supported natively by MuJoCo. If you want to save the model together with the UDD-state, you should use the get_xml or get_mjb methods on MjModel together with MjSim.get_state and save them with e.g. pickle.

Args: - file (IO stream): stream to write model to. - format: format to use (either ‘xml’ or ‘mjb’) - keep_inertials (bool): if False, removes all <inertial>

properties derived automatically for geoms by MuJoco. Note that this removes ones that were provided by the user as well.

set_state()

Sets the state from an MjSimState. If the MjSimState was previously unflattened from a numpy array, consider set_state_from_flattened, as the defensive copy is a substantial overhead in an inner loop.

Args: - value (MjSimState): the desired state. - call_forward: optionally call sim.forward(). Called by default if

the udd_callback is set.

set_state_from_flattened()

This helper method sets the state from an array without requiring a defensive copy.

step()

Advances the simulation by calling mj_step.

If qpos or qvel have been modified directly, the user is required to call forward() before step() if their udd_callback requires access to MuJoCo state set during the forward dynamics.

class mujoco_py.MjSimState

Represents a snapshot of the simulator’s state.

This includes time, qpos, qvel, act, and udd_state.

Attributes

Methods

mujoco_py.ignore_mujoco_warnings()

Class to turn off mujoco warning exceptions within a scope. Useful for large, vectorized rollouts.

PyMjData: Time-dependent data

PyMjData and related classes are automatically generated from the MuJoCo C header files. For more information on this process, see Autogenerated wrappers. Their structure therefore directly follows the MuJoCo structs.

class mujoco_py.PyMjData

Attributes

act

act_dot

active_contacts_efc_pos

actuator_force

actuator_length

actuator_moment

actuator_velocity

body_jacp

body_jacr

body_xmat

body_xpos

body_xquat

body_xvelp

body_xvelr

cacc

cam_xmat

cam_xpos

cdof

cdof_dot

cfrc_ext

cfrc_int

cinert

contact

crb

ctrl

cvel

efc_AR

efc_AR_colind

efc_AR_rowadr

efc_AR_rownnz

efc_D

efc_J

efc_JT

efc_JT_colind

efc_JT_rowadr

efc_JT_rownnz

efc_J_colind

efc_J_rowadr

efc_J_rownnz

efc_R

efc_aref

efc_b

efc_diagApprox

efc_force

efc_frictionloss

efc_id

efc_margin

efc_solimp

efc_solref

efc_state

efc_type

efc_vel

energy

geom_jacp

geom_jacr

geom_xmat

geom_xpos

geom_xvelp

geom_xvelr

light_xdir

light_xpos

maxuse_con

maxuse_efc

maxuse_stack

mocap_pos

mocap_quat

nbuffer

ncon

ne

nefc

nf

nstack

pstack

qLD

qLDiagInv

qLDiagSqrtInv

qM

qacc

qacc_unc

qacc_warmstart

qfrc_actuator

qfrc_applied

qfrc_bias

qfrc_constraint

qfrc_inverse

qfrc_passive

qfrc_unc

qpos

qvel

sensordata

set_joint_qpos

set_joint_qvel

set_mocap_pos

set_mocap_quat

site_jacp

site_jacr

site_xmat

site_xpos

site_xvelp

site_xvelr

solver

solver_fwdinv

solver_iter

solver_nnz

subtree_angmom

subtree_com

subtree_linvel

ten_length

ten_moment

ten_velocity

ten_wrapadr

ten_wrapnum

time

timer

userdata

warning

wrap_obj

wrap_xpos

xanchor

xaxis

xfrc_applied

ximat

xipos

Methods

get_body_jacp(name)

Get the entry in jacp corresponding to the body with the given name

get_body_jacr(name)

Get the entry in jacr corresponding to the body with the given name

get_body_ximat(name)

Get the entry in ximat corresponding to the body with the given name

get_body_xipos(name)

Get the entry in xipos corresponding to the body with the given name

get_body_xmat(name)

Get the entry in xmat corresponding to the body with the given name

get_body_xpos(name)

Get the entry in xpos corresponding to the body with the given name

get_body_xquat(name)

Get the entry in xquat corresponding to the body with the given name

get_body_xvelp(name)

Get the entry in xvelp corresponding to the body with the given name

get_body_xvelr(name)

Get the entry in xvelr corresponding to the body with the given name

get_cam_xmat(name)

Get the entry in xmat corresponding to the cam with the given name

get_cam_xpos(name)

Get the entry in xpos corresponding to the cam with the given name

get_camera_xmat(name)

Get the entry in xmat corresponding to the camera with the given name

get_camera_xpos(name)

Get the entry in xpos corresponding to the camera with the given name

get_geom_jacp(name)

Get the entry in jacp corresponding to the geom with the given name

get_geom_jacr(name)

Get the entry in jacr corresponding to the geom with the given name

get_geom_xmat(name)

Get the entry in xmat corresponding to the geom with the given name

get_geom_xpos(name)

Get the entry in xpos corresponding to the geom with the given name

get_geom_xvelp(name)

Get the entry in xvelp corresponding to the geom with the given name

get_geom_xvelr(name)

Get the entry in xvelr corresponding to the geom with the given name

get_joint_qpos(name)

Get the entry in qpos corresponding to the joint with the given name

get_joint_qvel(name)

Get the entry in qvel corresponding to the joint with the given name

get_joint_xanchor(name)

Get the entry in xanchor corresponding to the joint with the given name

get_joint_xaxis(name)

Get the entry in xaxis corresponding to the joint with the given name

get_light_xdir(name)

Get the entry in xdir corresponding to the light with the given name

get_light_xpos(name)

Get the entry in xpos corresponding to the light with the given name

get_mocap_pos(name)

Get the entry in pos corresponding to the mocap with the given name

get_mocap_quat(name)

Get the entry in quat corresponding to the mocap with the given name

get_site_jacp(name)

Get the entry in jacp corresponding to the site with the given name

get_site_jacr(name)

Get the entry in jacr corresponding to the site with the given name

get_site_xmat(name)

Get the entry in xmat corresponding to the site with the given name

get_site_xpos(name)

Get the entry in xpos corresponding to the site with the given name

get_site_xvelp(name)

Get the entry in xvelp corresponding to the site with the given name

get_site_xvelr(name)

Get the entry in xvelr corresponding to the site with the given name

MjSimPool: Batched simulation

class mujoco_py.MjSimPool

Keeps a pool of multiple MjSims and enables stepping them quickly in parallel.

Parameters:

sims : list of MjSim

List of simulators that make up the pool.

nsubsteps:

Number of substeps to run on step(). The individual simulators’ nsubstep will be ignored.

Attributes

Methods

static create_from_sim()

Create an MjSimPool by cloning the provided sim a total of nsims times. Returns the created MjSimPool.

Parameters:

sim : MjSim

The prototype to clone.

nsims : int

Number of clones to create.

forward()

Calls mj_forward on all simulations in parallel. If nsims is specified, than only the first nsims simulator are forwarded.

reset()

Resets all simulations in pool. If nsims is specified, than only the first nsims simulators are reset.

step()

Calls mj_step on all simulations in parallel, with nsubsteps as specified when the pool was created.

If nsims is specified, than only the first nsims simulator are stepped.

MjViewer: 3D rendering

class mujoco_py.MjViewerBasic(sim)

A simple display GUI showing the scene of an MjSim with a mouse-movable camera.

MjViewer extends this class to provide more sophisticated playback and interaction controls.

Parameters:

sim : MjSim

The simulator to display.

Attributes

Methods

render()

Render the current simulation state to the screen or off-screen buffer. Call this in your main loop.

class mujoco_py.MjViewer(sim)

Extends MjViewerBasic to add video recording, interactive time and interaction controls.

The key bindings are as follows:

• TAB: Switch between MuJoCo cameras.
• H: Toggle hiding all GUI components.
• SPACE: Pause/unpause the simulation.
• RIGHT: Advance simulation by one step.
• V: Start/stop video recording.
• T: Capture screenshot.
• I: Drop into ipdb debugger.
• S/F: Decrease/Increase simulation playback speed.
• C: Toggle visualization of contact forces (off by default).
• D: Enable/disable frame skipping when rendering lags behind real time.
• R: Toggle transparency of geoms.
• M: Toggle display of mocap bodies.

Parameters:

sim : MjSim

The simulator to display.

Attributes

Methods

render()

Render the current simulation state to the screen or off-screen buffer. Call this in your main loop.