Why is the same code not running now？

The environment that was once able to run successfully：

cantools==39.3.0
mqtt==0.0.1
paho-mqtt==1.6.1
pyserial==3.5
python-can==4.2.0

this is my code example,It was once able to run successfully.

# This is a sample Python script.
import asyncio
import time
from typing import List

import can
from can.notifier import MessageRecipient
# import cantools
import serial.tools.list_ports

# import paho.mqtt.client as mqtt
# import json

# client = mqtt.Client()
# db = cantools.database.load_file('.\wuling.dbc')


def on_connect(client, userdata, flags, rc):
    print(f"Connected with result code {rc}")


async def main() -> None:
    port = None
    ports_list = list(serial.tools.list_ports.comports())
    if len(ports_list) <= 0:
        print("无串口设备,即将退出...")
        time.sleep(2)
        exit(0)
    else:
        print("可用的串口设备如下：")
        for comport in ports_list:
            print(comport.name + "，描述：" + str(comport.description) + "，设备ID：" + str(comport.vid) + ":" + str(
                comport.pid))

        for comport in ports_list:
            if comport.pid == 4478 and comport.vid == 5840:
                print("选择第一个CAN设备：" + comport.name + " " + str(comport.description))
                port = comport
                break

    if port is None:
        print("未发现CAN设备,即将退出...")
        time.sleep(2)
        exit(0)

    # client.on_connect = on_connect
    # client.username_pw_set(username="user", password="user")
    # client.connect("127.0.0.1", 1883, 60)
    """The main function that runs in the loop."""

    with can.interface.Bus(bustype='slcan', channel=str(port.name), bitrate=500000, ) as bus:
        reader = can.AsyncBufferedReader()
        listeners: List[MessageRecipient] = [
            reader,
        ]
        loop = asyncio.get_running_loop()
        notifier = can.Notifier(bus, listeners, loop=loop)
        while True:
            msg = await reader.get_message()
            try:
                print(msg)
            except Exception as ex:
                print(ex)
                pass
            pass


if __name__ == "__main__":
    asyncio.run(main())