强制停止正在运行urllib下载的线程

import urllib.request
import threading

stop_flag = False

def download_file(url, filename):
    global stop_flag
    try:
        urllib.request.urlretrieve(url, filename)
    except urllib.error.URLError as e:
        print("下载出错：", e.reason)
    except urllib.error.HTTPError as e:
        print("HTTP错误：", e.code, e.reason)
    except Exception as e:
        print("其他错误：", str(e))
    finally:
        if stop_flag:
            print("下载已被中断")

def stop_download():
    global stop_flag
    stop_flag = True

url = "http://example.com/file.txt"
filename = "file.txt"
download_thread = threading.Thread(target=download_file, args=(url, filename))
download_thread.start()

stop_download()