This is a simple python script which is able to calculate digest from provided manifest.
Use it like this:
$ digest.py path/to/manifest.json
sha256:d7c67635d6bb320b17dbeed8bccc9261f61ab0bd4e81f3ecb34af899ea471ac0
Don't you have manifest? You can easily generate one:
$ ./generate_manifest.sh
This project also has very simple test suite (you should run it from root of the project):
$ PYTHONPATH="$PWD" py.test