Python gRPC shopping cart service
Keep-alive
Your sleep method is curious. There are alternates here:
https://stackoverflow.com/questions/20170251/how-to-run-the-python-program-forever
but those are generic to Python; there is a better option for gRPC:

In this case, you can call server.wait_for_termination() to cleanly block the calling thread until the server terminates.

Stopping
You should not only call it on KeyboardInterrupt; you should put it in a finally:
    server.start()
    try:
        # ...
    finally:
        server.stop(0)

This way, the server will be stopped if the user breaks with Ctrl+C, or if there is any other exception. However, I doubt it's necessary to call this at all if you use wait_for_termination.