I use ros-noetic inside a docker container with ubuntu 20.04
My project-tree loks like this:

catkin_ws
  |-src
    |-obstacle_detector
      |-src
        |-obstacle_detector.py
        |-yolo.py
      |-launch
          |-obstacle_detector.launch
      |-CMakeLists.txt
      |-package.xml

Inside a dockerfile I have:

COPY ./docker/entry-point.sh /
RUN chmod +x /entry-point.sh && 
    mkdir -p /root/catkin_ws/src/obstacle_detector/src/ && 
    mkdir -p /root/catkin_ws/src/obstacle_detector/launch/ && 
    mkdir -p /root/catkin_ws/src/obstacle_detector/data/
COPY ./src/* /root/catkin_ws/src/obstacle_detector/src/
COPY ./CMakeLists.txt /root/catkin_ws/src/obstacle_detector/
COPY ./package.xml /root/catkin_ws/src/obstacle_detector/
COPY ./launch/* /root/catkin_ws/src/obstacle_detector/launch/
COPY ./data/* /root/catkin_ws/src/obstacle_detector/data/

RUN apt update && 
    source "/opt/ros/$ROS_DISTRO/setup.bash" -- && 
    cd /root/catkin_ws && 
    apt install -y build-essential gcc && 
    catkin_make

My CMakeLists.txt:

cmake_minimum_required(VERSION 3.0.2)
project(obstacle_detector)

catkin_package(
)

include_directories(
)

catkin_install_python(PROGRAMS
  src/obstacle_detector.py
  src/yolo.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

install(DIRECTORY launch
  DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION})

entry-point.sh sources catkin_ws/devel/setup.sh

yolo.py contains a class Yolo.
obstacle_detector imports it and tries to use it.

catkin_make works without errors. But when I try to use roslaunch src/obstacle_detector/launch/obstacle_detector.launch I get an error: AttributeError: module 'yolo' has no attribute 'Yolo'

I have a very look-like example of a projects which actualy works and I don’t understand what is wrong here.

This is what’s inside of catkin_ws/devel/lib/obstacle_detector/yolo.py:

python_script = '/root/catkin_ws/src/obstacle_detector/src/yolo.py'
with open(python_script, 'r') as fh:
    context = {
        '__builtins__': __builtins__,
        '__doc__': None,
        '__file__': python_script,
        '__name__': __name__,
        '__package__': None,
    }
    exec(compile(fh.read(), python_script, 'exec'), context)

Thanks in advance.