Little Python Chat using websockets

#!/usr/bin/env python3
import asyncio
import datetime
import random
import websockets

USERS = set()

async def register(websocket):
        USERS.add(websocket)
        await broadcast_message("New User connected")

async def unregister(websocket):
        USERS.remove(websocket)
        await broadcast_message("A User disconnected")

async def broadcast_message(message, origin_websocket=None):
        if USERS:
                tag = "user"+str(id(origin_websocket)) if origin_websocket else "SYSTEM"
                tag = tag.ljust(15)
                if origin_websocket and len(USERS) < 2:
                        return
                await asyncio.wait([user.send("["+tag+"] "+message) for user in USERS if user is not origin_websocket]) 

async def chatroom(websocket, path):
        await register(websocket)
        print("NEW USER CONNECTED. Now: "+str(len(USERS)))
        try:
                async for message in websocket:
                        await broadcast_message(message, websocket)
        finally:
                await unregister(websocket)
                print("USER DISCONNECTED. Now: "+str(len(USERS)))

try:
        start_server = websockets.serve(chatroom, "0.0.0.0", "5000")

        asyncio.get_event_loop().run_until_complete(start_server)
        asyncio.get_event_loop().run_forever()
except KeyboardInterrupt:
        print("Stopped")
        pass