If you run the bananas-api as suggested in the readme using:

docker run --rm -p 127.0.0.1:8080:80 -p 127.0.0.1:1080:1080 -v "${BANANAS_COMMON}/local_storage:/code/local_storage" -v "${BANANAS_COMMON}/BaNaNaS:/code/BaNaNaS" openttd/bananas-api:local

Upload of a newgrf fails with the following error:

OSError: [Errno 18] Invalid cross-device link

The issue is that the temporary upload path and the local_storage path are not on the same physical device (one is inside the virtual file system of the docker container, while the other is on a volume mounted on the host).

According to the documentation I have found, shutil.move is the correct function to use if you are moving between file systems.