ROS2 之 使用 python Launch

用python写的launch文件可以启动和停止不同的节点，以及触发和操作各种事件。提供这个框架的包是launch_ros.   sudo apt install ros-foxy-launch-ros

通过 ros2 pkg create  --dependencies [deps] 会自动建立 launch 目录.

在 Python 中, 需要在 setup.py中加入data_files, 然后colcon 识别到 launch文件.

import os
from glob import glob
from setuptools import setup

package_name = 'my_package'

setup(
    # Other parameters ...
    data_files=[
        # ... Other data files
        # Include all launch files. This is the most important line
        (os.path.join('share', package_name), glob('launch/*.launch.py'))
    ]
)

然后建立 my_script.launch.py 文件. 这种文件和 launch 文件的规则不同, 

import launch
import launch.actions
import launch.substitutions
import launch_ros.actions

def generate_launch_description():
    return launch.LaunchDescription([
        launch.actions.DeclareLaunchArgument(
            'node_prefix',
            default_value=[launch.substitutions.EnvironmentVariable('USER'), '_'],
            description='Prefix for node names'),
        launch_ros.actions.Node(
            package='demo_nodes_cpp', executable='talker', output='screen',
            name=[launch.substitutions.LaunchConfiguration('node_prefix'), 'talker']),
    ])

然后使用 
    ros2 launch my_package script.launch.py