I’ve found it 
Here’s an example for the ldap3 library:
Pull the image
docker pull seatable/seatable-python-runner:latest
Activate a container and name it “add-libs” from the backend.
docker run -d --name="add-libs" seatable/seatable-python-runner custom
Enter the container
docker exec -it add-libs sh
Install the third-party package or do some other modification, quit the container after you finished.
/settings # pip install ldap3
You can add other Python libraries.
Exit the container
/settings # exit
Commit the new image
docker commit -m "add APPS" --change "CMD null" add-libs seatable/seatable-python-runner:APPS
Apply the new image
Modify the following variable in ./seatable_python.yml in the python-starter container:
PYTHON_RUNNER_IMAGE=seatable/seatable-python-runner:APPS
Up container:
docker-compose up -d
Purge:
docker stop add-libs && docker container rm add-libs
