rosrun Error:

Traceback (most recent call last):
File "/home/ving/catkin_ws/src/hello_tutorial/src/hello.py", line 3, in <module>
import rospy
File "/opt/ros/noetic/lib/python3/dist-packages/rospy/__init__.py", line 47, in <module>
from std_msgs.msg import Header
File "/opt/ros/noetic/lib/python3/dist-packages/std_msgs/msg/__init__.py", line 1, in <module>
from ._Bool import *
File "/opt/ros/noetic/lib/python3/dist-packages/std_msgs/msg/_Bool.py", line 6, in <module>
import genpy
File "/opt/ros/noetic/lib/python3/dist-packages/genpy/__init__.py", line 34, in <module>
from . message import Message, SerializationError, DeserializationError, MessageException, struct_I
File "/opt/ros/noetic/lib/python3/dist-packages/genpy/message.py", line 48, in <module>
import yaml
ImportError: No module named yaml

Reason: there are two versions of python locally
Check the current version: /usr/bin/python –version
Solution:

sudo ln -sf /usr/bin/python3 /usr/local/bin/python