An attempt to create the simplest "sane" HTTP Hello world in Python3

server.py

import http.server
import socketserver
from http import HTTPStatus

# custom server
class SimpleServer(socketserver.TCPServer):
    """Run a simple server."""
    def __init__(self, server_address, handler):
        # notify server starting up
        print('Server starting up ...')

        # set reuse address
        self.allow_reuse_address = True

        # call super constructor of socketserver.TCPServer class
        super().__init__(server_address, handler)

        # notify started
        print('Server now ready for requests!')

# create request handler
class RequestHandler(http.server.SimpleHTTPRequestHandler):
    def do_GET(self):
        self.send_response(HTTPStatus.OK)
        self.end_headers()
        self.wfile.write(b'Hello world')

# setup server vars
HOST, PORT = 'localhost', 9999

# Create the server, binding to localhost on port 9999
with SimpleServer((HOST, PORT), RequestHandler) as server:
    # Activate the server; this will keep running until you
    # interrupt the program with Ctrl-C
    server.serve_forever()