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Error when execute 'ros2 topic echo /hello_ros2 ros1_msgs/MyMsg'

The ros1_msgs/MyMsg is my custom message type, The package directory path is ~/ros1_install/src/ros1_msgs. So I open a terminal, then source the relevant package path to environment by this order:

ubuntu@cscsh:~$ ros2 topic echo /hello_ros2 ros1_msgs/MyMsg

ros2: command not found

ubuntu@cscsh:~$ source /opt/ros/melodic/setup.bash

ubuntu@cscsh:~$ source ~/ros1_install/devel/local_setup.bash(the install path of my custom message type package)

ubuntu@cscsh:~$ source /opt/ros/dashing/setup.bash

ubuntu@cscsh:~$ source ~/ros2_ws/install/local_setup.bash(the source code path of my ros2)

ROS_DISTRO was set to 'melodic' before. Please make sure that the environment does not mix paths from different distributions.

Then i execute the command:

dbt@cscsh-dubingtao:~$ ros2 topic echo /hello_ros2 ros1_msgs/MyMsg

Traceback (most recent call last): File "/home/dbt/ros2_ws/install/ros2cli/bin/ros2", line 11, in <module> load_entry_point('ros2cli==0.7.0', 'console_scripts', 'ros2')() File "/home/dbt/ros2_ws/install/ros2cli/lib/python3.6/site-packages/ros2cli/", line 69, in main rc = extension.main(parser=parser, args=args) File "/home/dbt/ros2_ws/install/ros2topic/lib/python3.6/site-packages/ros2topic/command/", line 43, in main return extension.main(args=args) File "/home/dbt/ros2_ws/install/ros2topic/lib/python3.6/site-packages/ros2topic/verb/", line 69, in main return main(args) File "/home/dbt/ros2_ws/install/ros2topic/lib/python3.6/site-packages/ros2topic/verb/", line 79, in main node.node, args.topic_name, args.message_type, callback) File "/home/dbt/ros2_ws/install/ros2topic/lib/python3.6/site-packages/ros2topic/verb/", line 109, in subscriber msg_module, topic_name, callback, qos_profile_sensor_data) File "/home/dbt/ros2_ws/install/rclpy/lib/python3.6/site-packages/rclpy/", line 1126, in create_subscription check_for_type_support(msg_type) File "/home/dbt/ros2_ws/install/rclpy/lib/python3.6/site-packages/rclpy/", line 20, in check_for_type_support ts = msg_type.__class__._TYPE_SUPPORT AttributeError: type object 'type' has no attribute '_TYPE_SUPPORT' This might be a ROS 1 message type but it should be a ROS 2 message type. Make sure to source your ROS 2 workspace after your ROS 1 workspace.

If i use the builtin message type, as i execute this command:

ros2 topic echo /hello_ros2 std_msgs/String

It work normally. so i check the PATH environment:

ubuntu@cscsh:~$ env | grep PYTHONPATH


The output is not just like the above, I only showed a part, you can see that ros2 uses python3.6, ros1 uses 2.7+, I think the problem maybe related to the Python version inconsistency?

Does anyone know the reason of the error message? Appreciate.