In order to keep codes generated from different protobuf on different folders, the protobuffers should be kept in different folders as well (grpc/grpc#9575 (comment))
To generate server and client python base code from the calculator protobuf:
python -m grpc_tools.protoc -I protobufs --python_out=. --grpc_python_out=. protobufs/calculator/calculator.proto
To generate server and client python base code from dummy trainer protobuf:
python -m grpc_tools.protoc -I protobufs --python_out=. --grpc_python_out=. /protobufs/trainer/dummy_trainer.proto