Python Requests.get不工作，无法建立新连接

我正在尝试一个网页抓取。一开始代码是有效的，但后来没有。代码是

import requests
import hashlib
from bs4 import BeautifulSoup

def sha512(x):
    m = hashlib.sha512(x.encode())
    return m.hexdigest()

session = requests.Session()
session.cookies["user-agent"] = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.117 Safari/537.36"

r = session.post("https://ringzer0ctf.com/login", data={"username":"myusername","password":"mypass"})
r = session.get("https://ringzeractf.com/challenges/13")

soup = BeautifulSoup(r.text, 'html.parser')

它给出了类似于

requests.exceptions.ConnectionError: HTTPSConnectionPool(host='ringzeractf.com', port=443): Max retries exceeded 
with url: /challenges/13 (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x04228490>: Failed to establish a new connection: [Errno 11001] getaddrinfo failed'))

requests.exceptions.ConnectionError:HTTPSConnectionPool（host='ringzeractf.com'，port=443）：超过最大重试次数
url为：/challenges/13（由NewConnectionError（“：未能建立新连接：[Errno 11001]getaddrinfo失败”）引起）

GET请求中的URL错误。将

ringzeractf

更改为

ringzer0ctf