提示res没有定义，实在找不出哪里的问题，求解答

import re  # 正则表达式库
import requests  # requests库

# from bs4 import BeautifulSoup  #BeautifulSoup库

# 百度图片网站链接
url = 'https://image.baidu.com/search/index'
keywords = input('请输入要查找的图片:')

# 网站参数
param = {
    'tn': 'baiduimage',
    'ps': 1,
    'ct': 201326592,
    'lm': -1,
    'cl': 2,
    'nc': 1,
    'ie': 'utf-8',
    'word': keywords
}

# 网站请求标头
header = {
    'Upgrade-Insecure-Requests': '1',
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Safari/537.36',
    'Access-Control-Allow-Credentials': 'true',
    'Connection': 'keep-alive',
    'Accept-Language': 'zh-CN,zh;q=0.9'
}

# 解析网站
r = requests.get(url, params=param, headers=header)
link = re.findall('"thumbURL":"(.*?)"', r.text)
count = 0

# 打印所有图片链接
for i in link:
    print(i)

# 保存图片
for j in link:
    count += 1
    res = requests.get(j, headers=header)
    with open('F:\桌面\图片\s{}.jpg'.format(count), 'wb') as fp:
        fp.write(res.content)
r.close()
res.close()

说明正则式没找到内容，link是空的，所以，res没有赋值
你在循环之前，打印一下link看看找到东西没