GitLab 10.0 added an API route to download a single artifact file:

GET /projects/:id/jobs/:job_id/artifacts/*artifact_path

Example request:

curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" \
    "https://gitlab.example.com/api/v4/projects/1/jobs/5/artifacts/some/release/file.pdf"

python-gitlab does not appear to support this.

I imagine something like this:

job.get_artifact('some/release/file.pdf', streamed=True, action=whatever)