There is a full Python client for NiFi, NiFi-Registry, and I'm just about to add the Schema-Registry as well.
https://github.com/Chaffelson/nipyapi
It is community supported and comes with all the basic calls you would need to automate your NiFi flows, higher level functions for complex tasks like 'stop all processors in this process group and purge all the queues', and demos of various usage methods like tokenAuth security, promoting flow versions between environments, and deploying NiFi in Docker containers for testing.