Error when running rqt_graph. No module named "error"

edit

I'm running my model on ROS melodic.

Followed this tutorial to watch my dynamic graph of topics and nodes: http://wiki.ros.org/ROS/Tutorials/Und...

when I run rosrun rqt_graph rqt_graph I get an error:

File "/opt/ros/melodic/lib/python2.7/dist-packages/roslib/launcher.py", line 42, in <module>
    import rospkg
ModuleNotFoundError: No module named 'rospkg'

In order to fix it I changed my PYTHONPATH as it suggested to do in this issue: https://answers.ros.org/question/2432... (But I don't use anaconda though)

Then I got another error:

File "/usr/lib/python2.7/dist-packages/yaml/__init__.py", line 2, in <module>
    from error import *
ModuleNotFoundError: No module named 'error'

How can I fix that?

EDIT: I figured out that it is related to python version, I use python3.7.6 What version should I use instead? I tried 2.7.13 and it did not help