如何实现每次请求更换user_agent？

Question

以这种遍历的方式爬信息，应该是每遍历一个地址都对应有一次请求吧，那每次请求的时候也应该是随机的请求头才对，但是我设置的随机请求头在遍历range(5, 1000)整个过程从来没有换过user_agent，只有重新运行程序才会出现新的user_agent。所以我对这个随机请求头有什么误解吧！还是range(5, 1000)只发生了一次请求？如何实现随每次请求更换user_agent呢？（单个爬虫，非框架）

user_agent = [
    "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_8; en-us) AppleWebKit/534.50 (KHTML, like Gecko) Version/5.1 Safari/534.50",
    "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-us) AppleWebKit/534.50 (KHTML, like Gecko) Version/5.1 Safari/534.50",
    "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0"]

headers = {'User-Agent': random.choice(user_agent)}

urls = [f'https://api.bilibili.com/x/web-interface/view?aid={av_num}' for av_num in range(5, 1000)]

for url in urls:
    response = requests.request("get", url, headers=headers)
    print(headers)

Answer 1

当程序运行到

headers = {'User-Agent': random.choice(user_agent)}

_这里时，choice函数会随机挑选一个请求头，将它赋值给headers，从此headers的值就确定下来了。
如果需要随机更换请求头，需要把上面的语句移至for循环之内。更改后的代码如下：

import requests
import random

user_agent = [
    "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_8; en-us) AppleWebKit/534.50 (KHTML, like Gecko) Version/5.1 Safari/534.50",
    "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-us) AppleWebKit/534.50 (KHTML, like Gecko) Version/5.1 Safari/534.50",
    "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0"]


urls = [f'https://api.bilibili.com/x/web-interface/view?aid={av_num}' for av_num in range(5, 1000)]

for url in urls:
    headers = {'User-Agent': random.choice(user_agent)}
    response = requests.request("get", url, headers=headers)
    print(headers)