【Python】解决urllib返回http error 503问题

想自动下载一些网页，写了个简单的爬虫，但是碰到了503问题。

代码是下面这个样子：

    site = "http://XXXX"
    local_filename, headers = urllib.request.urlretrieve(site)
    html = open(local_filename, encoding='UTF-8')

    soup = bs4.BeautifulSoup(html)
    names = soup.find_all('a')

过去都会像上面这样写，不过这次调用urlretrieve的时候返回了503，解决方法是用下面这样的代码，模拟浏览器的行为去访问。

    hdr = {
        'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.121 Safari/537.36',
        'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9',
        'Accept-Charset': 'ISO-8859-1,utf-8;q=0.7,*;q=0.3',
        'Accept-Encoding': 'gzip, deflate, br',
        'Accept-Language': 'zh-CN,zh;q=0.9',
        'Connection': 'keep-alive'}

    site = "https://XXXX"

    r = urllib.request.Request(site, headers=hdr)
    response = urllib.request.urlopen(r)
    page = response.read()

    buff = BytesIO(page)
    f = gzip.GzipFile(fileobj=buff)
    res = f.read().decode('utf-8')

    soup = bs4.BeautifulSoup(res, 'html.parser')
    names = soup.find_all('a')