Python stub files allow to supply type-hinting information for binary Python modules (e.g. pybind-based).
In rosbag2_py stub files are generated with utility called stubgen.
To regenerate stub files
cd <workspace>
colcon build --packages-up-to rosbag2_py
source install/setup.sh
# Make sure rosbag2_py can be imported
python3 -c 'import rosbag2_py'
sudo apt update && sudo apt install mypy=0.942-1ubuntu1
cd <rosbag2 git repo>
stubgen -p rosbag2_py -o rosbag2_py