Ros2 can not import python modules located in subfolders

Question

I am new to use ROS. I use Ros2 Humble on Ubuntu 22.04. I need to import some python codes/modules from different nested folders (or nested nested folders) to a Ros2 python node. The Ros2 node (demo_in_ros.py) is located in src folder of my Ros package. I have all other python modules in src folder as well. I have imported all python modules to the Ros2 node (demo_in_ros.py) using the python import function (example: from utils import common_utils). The structure of my Ros2 package is below:

ros2demo_ws
    |src
        |dl_demo
            |dl_demo
                |demo_in_ros.py
                |utils
                    |common_utils.py

I have successfully built the package using colcon build. After running ros2 run dl_demo pub_sub, I get this error:

   from utils import common_utils
ModuleNotFoundError: No module named 'utils'

How can I solve this issue?

I appreciate any help in advance.

Thanks,

Abbas