Overview
Gazebo provides a Python API to interact with the world.
For now, we provide a TestFixture class that allows to load a world file, step simulation and check entities and components.
- Step 1: Load a world with a fixture
file_path = os.path.dirname(os.path.realpath(__file__))
fixture = TestFixture(os.path.join(file_path, 'gravity.sdf'))
- Step 2: Write your
preupdate, update or postupdate code:
def on_post_udpate_cb(_info, _ecm):
...
- Step 3: Register the function.
fixture.on_post_update(on_post_udpate_cb)
- Step 4: Be sure to call finalize before running the server.
server.run(True, 1000, False)
Run the example
In the examples/scripts/python_api folder there is a Python script that shows how to make use of this API.
If you compiled Gazebo from source you should modify your PYTHONPATH:
export PYTHONPATH=$PYTHONPATH:<path to ws>/install/lib/python
Now you can run the example:
$ python3 examples/scripts/python_api/testFixture.py
[Msg] Loading SDF world file[/home/ahcorde/gz_fortress/src/ign-gazebo/examples/scripts/python_api/gravity.sdf].
[Dbg] [Physics.cc:789] Loaded [gz::physics::dartsim::Plugin] from library [/home/ahcorde/gz_fortress/install/lib/gz-physics-5/engine-plugins/libgz-physics-dartsim-plugin.so]
[Dbg] [SimulationRunner.cc:909] Loaded system [gz::sim::systems::Physics] for entity [1]
[Msg] Loaded level [3]
[Msg] Serving world controls on [/world/gravity/control], [/world/gravity/control/state] and [/world/gravity/playback/control]
[Msg] Serving GUI information on [/world/gravity/gui/info]
[Msg] World [gravity] initialized with [default_physics] physics profile.
[Msg] Serving world SDF generation service on [/world/gravity/generate_world_sdf]
[Msg] Serving world names on [/gazebo/worlds]
[Msg] Resource path add service on [/gazebo/resource_paths/add].
[Msg] Resource path get service on [/gazebo/resource_paths/get].
[Msg] Resource paths published on [/gazebo/resource_paths].
[Msg] Found no publishers on /stats, adding root stats topic
[Msg] Found no publishers on /clock, adding root clock topic
[Dbg] [SimulationRunner.cc:524] Creating PostUpdate worker threads: 2
[Dbg] [SimulationRunner.cc:537] Creating postupdate worker thread (0)
AddSystem1
World entity is 1
Gravity 0 0 -9.8
Entity for falling model is: 4
AddSystem2
iterations 1000
post_iterations 1000
pre_iterations 1000
Gazebo Systems written in Python
Gazebo also provides a way to write systems in Python. This is done using the gz::sim::systems::PythonSystemLoader system which loads a given python module specified by its <module_name> parameter. The search path for the module includes GZ_SIM_SYSTEM_PLUGIN_PATH as well as PYTHONPATH. The module is expected to provide a function called get_system that returns an instance of a class that implements the various interfaces in gz::sim::System.
Example python system:
from gz.math8 import Vector3d
from gz.sim9 import Model, Link
import random
class TestSystem(object):
def __init__(self):
self.id = random.randint(1, 100)
def configure(self, entity, sdf, ecm, event_mgr):
self.model = Model(entity)
self.link = Link(self.model.canonical_link(ecm))
print("Configured on", entity)
print("sdf name:", sdf.get_name())
self.force = sdf.get_double("force")
print(f"Applying {self.force} N on link {self.link.name(ecm)}")
def pre_update(self, info, ecm):
if info.paused:
return
if info.iterations % 3000 == 0:
self.link.add_world_force(
ecm, Vector3d(0, 0, self.force),
Vector3d(random.random(), random.random(), 0))
def get_system():
return TestSystem()
The system can be added to SDFormat model or world with:
<plugin filename="gz-sim-python-system-loader-system"
name="gz::sim::systems::PythonSystemLoader">
<module_name>test_system</module_name>
<force>100</force>
</plugin>
asuming the name of the module is test_system and the directory containing the module has been added to GZ_SIM_SYSTEM_PLUGIN_PATH,
