Topic parameter 'data_class' is not initialized

[ElonKou]

Hi,
When I use rqt_bag to record a topic, some of the topics cannot be recorded and a warning is displayed, but when I use the command line tool rosbag, these topics can be recorded.
I am working under ubuntu16.04

[WARN] [1553769837.934367]: Error subscribing to /huace/nmea_sentence (ignoring): topic parameter 'data_class' is not initialized
[WARN] [1553769838.267172]: Error subscribing to /lslidar_sweep (ignoring): topic parameter 'data_class' is not initialized
[WARN] [1553769838.271660]: Error subscribing to /lslidar_packet0 (ignoring): topic parameter 'data_class' is not initialized
[WARN] [1553769838.277671]: Error subscribing to /tong/nmea_sentence (ignoring): topic parameter 'data_class' is not initialized
[WARN] [1553769838.285201]: Error subscribing to /lslidar_packet1 (ignoring): topic parameter 'data_class' is not initialized

I checked the corresponding code and found that the function could not get their correct type for the topic of the previous problem.
pytype = roslib.message.get_message_class(datatype)

Can you help me determine what is going on in the end, how to solve it, thank you very much.

[Guozhongyuan]

Because rospy cannot find the msg description.

You can copy msg file and import it,

import os
import sys
sys.path.append('./devel/lib/python3/dist-packages')
from your_msgs.msg import *

Or another method is to source devel/setup.bash before run python file.