The author of this series of tutorials ： Little fish
official account ： Fish fragrance ROS
QQ Communication group ：139707339
Teaching video address ： Small fish B standing
Full document address ： Fish fragrance ROS Official website
Copyright notice ： Reprint and commercial use are prohibited unless permitted .
python Compared with the way of introducing dependencies C++ It's too easy . In this section, Xiaoyu takes you to learn from a few examples Python Path lookup mechanism for .
stay d2lros2/d2lros2/chapt2/basic newly build second_ros2_node.py, Enter the following
# Import rclpy library , If Vscode It doesn't matter to show red wavy lines
# We just put VsCode Just a notepad , Who cares what Notepad thinks about code , isn't it? ？
import rclpy
from rclpy.node import Node
# call rclcpp Initialization function for
rclpy.init()
# call rclcpp Run the loop we created second_node node
rclpy.spin(Node("second_node"))
Open the terminal , Input instruction
ls
python3 second_ros2_node.py
Open a new terminal , Input
ros2 node list
perfect , Four lines of code write a ROS2 Of Python node .
So here comes the question , We import rclpy,rclpy Where is it ？python How did you find it ？
Python3 function import rclpy How did you find it ？ The answer is through the environment variable PYTHONPATH
Ctrl+C Interrupt node operation , Then enter the following command
echo $PYTHONPATH
result
/opt/ros/humble/lib/python3.10/site-packages:/opt/ros/humble/local/lib/python3.10/dist-packages
You will find that there is something about humble Of python route , Look under the above two directories rclpy, See if you can find rclpy
Find the first path
ls -l /opt/ros/humble/lib/python3.10/site-packages | grep rclpy
Did not find , the second
ls -l /opt/ros/humble/local/lib/python3.10/dist-packages/ | grep rclpy
eureka
drwxr-xr-x 1 root root 4096 Jun 3 04:45 rclpy
drwxr-xr-x 2 root root 4096 May 23 22:23 rclpy-3.3.4-py3.10.egg-info
Use unset Directive can delete environment variables , Try deleting PYTHONPATH Then run the code , See if you can still import rclpy.
unset
python3 second_ros2_node.py
The tips are as follows
[email protected]:~/d2lros2/d2lros2/chapt2/basic# python3 second_ros2_node.py
Traceback (most recent call last):
File "/root/d2lros2/d2lros2/chapt2/basic/second_ros2_node.py", line 3, in <module>
import rclpy
ModuleNotFoundError: No module named 'rclpy'
Please remember this error message ModuleNotFoundError: No module named 'xxx', This is what you may often encounter in your future study .
Next When encountered for the first time , You will think of the article "little fish" , Then smile scornfully at it , Then find the directory where the library is located , Add it to the environment .
In this section, Xiaoyu took you to learn Python To write ROS2 How nodes work , And bring you to know a common mistake ModuleNotFoundError: No module named 'xxx'.
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