python 爬虫爬取网页遇到403问题

示例代码：<python3版本>

import urllib
import urllib.request
import random

my_headers=[
"Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36",
"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36",
"Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0",
"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/537.75.14",  
"Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Win64; x64; Trident/6.0)"
]  

url = "https://www.whatismyip.com/"

randdom_header=random.choice(my_headers)  
 
req = urllib.request.Request(url)

req.add_header("User-Agent",randdom_header)
req.add_header("GET",url)

response = urllib.request.urlopen(req)
html = response.read().decode('utf-8')
print(html)