This is a Python library implementing the rpcplugin protocol, allowing an application written in Python to consume plugins as a client, or allowing plugin servers to be written in Python.
The rpcplugin protocol is a low-level protocol built around gRPC. If you're intending to write a plugin for an application that uses this protocol, check first to see if that application offers an application-specific Python SDK that wraps this library, so you can avoid dealing with low-level gRPC details and Protocol Buffers definitions.