ROS 2 create node - python subscriber

因為在ROS 2 python 程式的建立方式跟以往很不同，所以紀錄ROS 2 ardent 版本下

如何建立python 程式

python 程式可以加速POC，例如用python 的繪圖

https://github.com/ros2/examples/tree/master/rclpy/topics/minimal_subscriber

ROS 2 的python package 無法跟c++的放同一個

建立package

cd ~/ros2_ws/src mkdir karl_demo_py cd karl_demo_py

建立subscriber 程式

import rclpy import matplotlib.pyplot as plt from karl_demo.msg import Custom g_node = None def callback(msg):     plt.clf()     plt.plot(msg.data)     plt.draw()     plt.pause(0.001) def main(args=None)     global g_node           rclpy.init(args=args)     g_node = rclpy.create_node('listener')           sub = g_node.create_subscription(Custom, 'test', callback)     sub # prevent unused variable warning     while rclpy.ok():         rclpy.spin_once(g_node)     g_node.destroy_node()     rclpy.shutdown() if __name__ == '__main__':     plt.ion()     plt.show()     main()

編輯package.xml 、setup.py 及setup.cfg

沒有這些檔案的話，python 檔案無法link 到ROS 2

setup.cfg 則是幫助把檔案放到worspace/lib/karl_demo_py 內，這樣ROS 2 指令才會找到這個檔案才能執行

cd ~/ros2_ws/src/karl_demo_py vim package.xml vim setup.py vim setup.cfg

package.xml

<?xml version="1.0"?> <?xml-model href="http://download.ros.org/schema/package_format2.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?> <package format="2">   <name>examples_rclpy_minimal_subscriber</name>   <version>0.4.0</version>   <description>Examples of minimal subscribers using rclpy.</description>   <maintainer email="mikael@osrfoundation.org">Mikael Arguedas</maintainer>   <license>Apache License 2.0</license>   <exec_depend>rclpy</exec_depend>   <exec_depend>karl_demo</exec_depend>   <export>     <build_type>ament_python</build_type>   </export> </package>

以下註解的地方，是可以省略的部分

Setup.py

from setuptools import setup package_name = 'karl_demo_py' setup(     name=package_name,     packages=[],     py_modules=['listener',],     install_requires=['setuptools'],     #author='Mikael Arguedas',     #author_email='mikael@osrfoundation.org',     #maintainer='Mikael Arguedas',     #maintainer_email='mikael@osrfoundation.org',     #keywords=['ROS'],     #classifiers=[     #    'Intended Audience :: Developers',     #    'License :: OSI Approved :: Apache Software License',     #    'Programming Language :: Python',     #    'Topic :: Software Development',     #],     #description='Examples of minimal subscribers using rclpy.',     #license='Apache License, Version 2.0',     #tests_require=['pytest'],     entry_points={         'console_scripts': [             'subscriber_old_school = subscriber_old_school:main',             'subscriber_lambda = subscriber_lambda:main',             'subscriber_member_function = subscriber_member_function:main',         ],     }, )

Setup.cfg

[develop] script-dir=$base/lib/karl_demo_py [install] script-dir=$base/lib/karl_demo_py

最後執行前，記得安裝python 套件 

在ROS ，matplotlib 有裝在ROS 的目錄內，所以可以直接用

但在ROS 2 沒有

sudo apt-get install python3-matplotlib cd ~/ros2_ws source install/setup.bash ros2 run karl_demo_py listener.py