Ошибка запуска примера кода библиотеки Python Websocket

Question

У меня ошибка с предоставленным примером кода, и я ничего не нашел в Google, вот трассировка

ERROR:websockets.server:Error in connection handler
Traceback (most recent call last):
  File "C:\Users\felix\AppData\Local\Programs\Python\Python36\lib\site-packages\websockets\server.py", line 84, in handler
    yield from self.ws_handler(self, path)
  File "C:\Users\felix\Desktop\letistry\server.py", line 45, in counter
    async for message in websocket:
TypeError: 'async for' requires an object with __aiter__ method, got WebSocketServerProtocol

Все, что я сделал, это скопировал и вставил код из https://websockets.readthedocs.io/en/stable/intro.html

я запускаю пример синхронизации (код приведен ниже) на python 3.6 в windows 10.

#!/usr/bin/env python

# WS server example that synchronizes state across clients

import asyncio
import json
import logging
import websockets

logging.basicConfig()

STATE = {'value': 0}

USERS = set()

def state_event():
    return json.dumps({'type': 'state', **STATE})

def users_event():
    return json.dumps({'type': 'users', 'count': len(USERS)})

async def notify_state():
    if USERS:       # asyncio.wait doesn't accept an empty list
        message = state_event()
        await asyncio.wait([user.send(message) for user in USERS])

async def notify_users():
    if USERS:       # asyncio.wait doesn't accept an empty list
        message = users_event()
        await asyncio.wait([user.send(message) for user in USERS])

async def register(websocket):
    USERS.add(websocket)
    await notify_users()

async def unregister(websocket):
    USERS.remove(websocket)
    await notify_users()

async def counter(websocket, path):
    # register(websocket) sends user_event() to websocket
    await register(websocket)
    try:
        await websocket.send(state_event())
        async for message in websocket:
            data = json.loads(message)
            if data['action'] == 'minus':
                STATE['value'] -= 1
                await notify_state()
            elif data['action'] == 'plus':
                STATE['value'] += 1
                await notify_state()
            else:
                logging.error(
                    "unsupported event: {}", data)
    finally:
        await unregister(websocket)

asyncio.get_event_loop().run_until_complete(
    websockets.serve(counter, 'localhost', 6789))
asyncio.get_event_loop().run_forever()