launch-generator

The package launch-generator is a tool to easily generate launch descriptions for ROS 2. It is based on the launch and launch_ros packages.

Installation

pip install launch-generator

Usage

Generator is the main class of the package. It is used to generate launch descriptions. It can add some actions with the add_* methods and generate the launch description with the generate_launch_description method. add_* methods arguments are the same as the original basically. add_group() and add_container() methods return a generator object that can be used to add internal actions to the group or container.

from launch import LaunchDescription
import launch_generator

def generate_launch_description() -> LaunchDescription:
    gen = launch_generator.Generator()

    # Add launch arguments
    arg_configuration = gen.add_arg('arg_name', 'default_value')

    # Add nodes and use the launch arguments
    node = gen.add_node('executable_name', 'package_name', name=arg_configuration)

    # Include other launch files
    include = gen.include_launch('package_name', 'launch/file/path.launch.py')

    # Add group
    group = gen.add_group('namespace')

    # Add nodes to group
    group.add_node('executable_name', 'package_name')

    return LaunchDescription(gen.generate_launch_description())

Migration

imports

launch_ros

from launch import LaunchDescription
from launch_ros.actions import *
from launch_ros.substitutions import *
...

launch_generator

from launch import LaunchDescription
import launch_generator

Argument

launch_ros

# declare argument
arg = launch.actions.DeclareLaunchArgument(name,
                                           default_value=default_value,
                                           description=description,
                                           choices=choices)

# use argument
Node(
    ...
    parameters=[{'param_name': launch.substitutions.LaunchConfiguration(name)}]
)

# add argument to launch description
return LaunchDescription([arg, ...])

launch_generator

arg = gen.add_arg(name, default_value, description, choices)

Node(
    ...
    parameters=[{'param_name': arg}]
)

return LaunchDescription(gen.generate_launch_description())

Node

launch_ros

Node(
    package=package,
    executable=executable,
    name=name,
    namespace=namespace,
    parameters=parameters,
    remappings=remappings,
    arguments=arguments,
    **kwargs
)

# add node to launch description
return LaunchDescription([node, ...])

launch_generator

node = gen.add_node(executable, package, name, namespace, parameters=parameters, remappings=remappings, ros_arguments=arguments, **kwargs)

return LaunchDescription(gen.generate_launch_description())

IncludeLaunchDescription

launch_ros

package_path = FindPackageShare('package_name').find('package_name')
launch_file_path = os.path.join(package_path, 'launch', 'file_name.launch.py')
include = IncludeLaunchDescription(
    launch.launch_description_sources.PythonLaunchDescriptionSource(launch_file_path),
)

# add include to launch description
return LaunchDescription([include, ...])

launch_generator

gen.add_include_launch_description('package_name', 'launch/file_name.launch.py')

return LaunchDescription(gen.generate_launch_description())

GroupAction

launch_ros

group = GroupAction(
    actions=[
        PushRosNamespace(
            namespace=namespace,
        ),
        Node(
            ...
        ),
        Node(
            ...
        ),
    ]
)

# add group to launch description
return LaunchDescription([group, ...])

launch_generator

group = gen.add_group(namespace)
group.add_node(...)
group.add_node(...)

return LaunchDescription(gen.generate_launch_description())

Composable node container

launch_ros

container = ComposableNodeContainer(
    name=name,
    namespace=namespace,
    package='rclcpp_components',
    executable='component_container',
    composable_node_descriptions=[
        ComposableNode(...),
        ComposableNode(...),
    ],
)

# add container to launch description
return LaunchDescription([container, ...])

launch_generator

container = gen.add_container(name, namespace)
container.add_composable_node(...)
container.add_composable_node(...)

return LaunchDescription(gen.generate_launch_description())

Composable node

launch_ros

node = ComposableNode(
    package=package,
    plugin=plugin,
    name=name,
    namespace=namespace,
    parameters=parameters,
    remappings=remappings,
    extra_arguments=extra_arguments,
)

return LaunchDescription([node, ...])

launch_generator

node = container.add_composable_node(package, plugin, name, namespace, parameters, remappings, extra_arguments)

return LaunchDescription(gen.generate_launch_description())

Load composable nodes to existing container

launch_ros

load_composable_nodes = LoadComposableNodes(
    target_container='target_container_name',
    composable_node_descriptions=[
        ComposableNode(...),
        ComposableNode(...),
    ],
)

return LaunchDescription([load_composable_nodes, ...])

launch_generator

load_composable_nodes = gen.add_load_composable_nodes('target_container_name', [
    gen.add_composable_node(...),
    gen.add_composable_node(...),
])

return LaunchDescription(gen.generate_launch_description())

Register Event Handler

launch_ros

register_event_handler = RegisterEventHandler(
    event_handler=OnProcessExit(
        target_action=target_node,
        on_exit=[other_node],
    ),
)

return LaunchDescription([register_event_handler, ...])

launch_generator

on_exit = gen.add_register_event_handler(target_node, launch_generator.EventTriggerType.ON_EXIT)
on_exit.add_action(executable, package, name)

return LaunchDescription(gen.generate_launch_description())

Ros timer

launch_ros

timer = RosTimer(
    period=period,
    actions=[
        Node(
            ...
        ),
        Node(
            ...
        ),
    ]
)

return LaunchDescription([timer, ...])

launch_generator

timer = gen.add_ros_timer(period)
timer.add_node(...)
timer.add_node(...)

return LaunchDescription(gen.generate_launch_description())

Set parameter

launch_ros

set_parameter = SetParameter(
    name=name,
    value=value,
)

return LaunchDescription([set_parameter, ...])

launch_generator

gen.add_set_parameter(name, value)

return LaunchDescription(gen.generate_launch_description())

Set parameter file

launch_ros

package_path = FindPackageShare('package_name').find('package_name')
config_file_path = os.path.join(package_path, 'config', 'file_name.yaml')
set_parameter_file = SetParameterFile(config_file_path)

return LaunchDescription([set_parameter_file, ...])

launch_generator

gen.add_set_parameter_file('package_name', 'config/file_name.yaml')

return LaunchDescription(gen.generate_launch_description())

Set remap

launch_ros

set_remap = SetRemap(
    src=src_topic,
    dst=dst_topic,
)

return LaunchDescription([set_remap, ...])

launch_generator

gen.add_set_remap(src_topic, dst_topic)

return LaunchDescription(gen.generate_launch_description())

Set environment variable

launch_ros

set_env = SetEnvironmentVariable(
    name=name,
    value=value,
)

return LaunchDescription([set_env, ...])

launch_generator

gen.add_set_environment_variable(name, value)

return LaunchDescription(gen.generate_launch_description())

Other entities

add_action() supports all the entities of launch and launch_ros packages.

launch_ros

ns = PushRosNamespace(
    namespace=namespace,
)

return LaunchDescription([ns, ...])

launch_generator

gen.add_action(PushRosNamespace(namespace))

return LaunchDescription(gen.generate_launch_description())

Utilities

condition()

condition() is a function to create IfCondition or UnlessCondition object.

arg = gen.add_arg(name, default_value, description, choices)

# basic usage
gen.add_node('executable_name', 'package_name',
             condition=launch_generator.condition(arg)) # the node is launched only if arg is 'True' or 'true'

# reverse condition
gen.add_node('executable_name', 'package_name',
             condition=launch_generator.condition(arg, reverse=True)) # the node is launched only if arg is 'False' or 'false'

# python expression can be used
gen.add_node('executable_name', 'package_name',
             condition=launch_generator.condition([arg, '< 10'])) # the node is launched only if arg is less than 10

arg2 = gen.add_arg(name, default_value, description, choices)
# multiple conditions can be used
gen.add_node('executable_name', 'package_name',
             condition=launch_generator.condition([arg, '< 10 or ', arg2])) # the node is launched only if arg is less than 10 or greater than 20

load_param_file()

load_param_file() is a function to load a yaml file to parameter dictionary. The function can replace the value of parameters written in the form of $(arg arg_name) like subst_value of ROS1 with LaunchConfiguration(arg_name).

Example of yaml file:

node_name:
    ros__parameters:
        param1: $(arg arg_name)
        param2:
            sub1: prefix_$(arg arg_name)
            sub2: $(arg arg_name)_suffix
            sub3: $(arg arg_name)_$(arg_name2)

arg = gen.add_arg('arg_name', 'default_value')
arg2 = gen.add_arg('arg_name2', 'default_value')
param_dict = launch_generator.load_param_file('package_name', 'config/file_name.yaml')

# param_dict = {
#     'node_name': {
#         'ros__parameters': {
#             'param1': launch.substitutions.LaunchConfiguration('arg_name'),
#             'param2': {
#                 'sub1': ['prefix_', launch.substitutions.LaunchConfiguration('arg_name')],
#                 'sub2': [launch.substitutions.LaunchConfiguration('arg_name'), '_suffix'],
#                 'sub3': [launch.substitutions.LaunchConfiguration('arg_name'), '_', launch.substitutions.LaunchConfiguration('arg_name2')],
#             }
#         }
#     }
# }

gen.add_node('executable_name', 'package_name', parameters=[param_dict['node_name']['ros__parameters']])

return LaunchDescription(gen.generate_launch_description())

Name		Name	Last commit message	Last commit date
Latest commit History 44 Commits
.github/workflows		.github/workflows
src/launch_generator		src/launch_generator
test		test
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
pyproject.toml		pyproject.toml
setup.py		setup.py

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Repository files navigation

launch-generator

Installation

Usage

Migration

imports

Argument

Node

IncludeLaunchDescription

GroupAction

Composable node container

Composable node

Load composable nodes to existing container

Register Event Handler

Ros timer

Set parameter

Set parameter file

Set remap

Set environment variable

Other entities

Utilities

condition()

load_param_file()

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launch-generator

Installation

Usage

Migration

imports

Argument

Node

IncludeLaunchDescription

GroupAction

Composable node container

Composable node

Load composable nodes to existing container

Register Event Handler

Ros timer

Set parameter

Set parameter file

Set remap

Set environment variable

Other entities

Utilities

condition()

load_param_file()