第一天学python爬虫，User-Agent报错

代码：
import requests
import re
import time

#请求函数

def request_get(url, ret_type="text", timeout=5, encoding="GBK"):
headers = {
"User-Agent": Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36
}
res = requests.get(url=url, headers=headers, timeout=timeout)
res.encoding = encoding
if ret_type == "text":
return res.text
elif ret_type == "image":
return res.content

报错如下：
File "D:\test\test.py", line 10
"User-Agent": Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36

SyntaxError: invalid syntax. Perhaps you forgot a comma?

headers = {
'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36'
}

后面的字符串需要引起来

楼上的回答了，值是字符串，需要引号引起来。 建议下次贴代码时， 用插入代码功能