当需要登录时，如何使用urllib的urlopen保存文件？

import urllib.request

login_url = "https://example.com/login"  # 替换为实际的登录URL
username = "your_username"  # 替换为实际的用户名
password = "your_password"  # 替换为实际的密码

login_data = {
    "username": username,
    "password": password
}

login_request = urllib.request.Request(login_url, data=urllib.parse.urlencode(login_data).encode())

login_response = urllib.request.urlopen(login_request)

login_cookie = login_response.headers.get("Set-Cookie")

file_url = "https://example.com/file"  # 替换为实际的文件URL

file_request = urllib.request.Request(file_url)
file_request.add_header("Cookie", login_cookie)

file_response = urllib.request.urlopen(file_request)

with open("filename.ext", "wb") as file:
    file.write(file_response.read())