import requests
from lxml import etree

headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.92 Safari/537.36',
          'Cookie': 'gr_user_id = c6f58a39 - ea25 - 4f58 - b448 - 545070192c4e;59a81cc7d8c04307ba183d331c373ef6_gr_session_id = e8e4b66f - 440a - 4ae7 - a76a - fe2dd2b34a26;59a81cc7d8c04307ba183d331c373ef6_gr_last_sent_sid_with_cs1 = e8e4b66f - 440a - 4ae7 - a76a - fe2dd2b34a26;59a81cc7d8c04307ba183d331c373ef6_gr_last_sent_cs1 = N % 2FA;59a81cc7d8c04307ba183d331c373ef6_gr_session_id_e8e4b66f - 440a - 4ae7 - a76a - fe2dd2b34a26 = true;grwng_uid = 9ec14ad9 - 5ac0 - 4bb1 - 81c1 - bc60d2685710;abtest_ABTest4SearchDate = b;xzuuid = 79426b52;_uab_collina = 154660443606130958890473;TY_SESSION_ID = 907f32df - c060 - 49ca - b945 - 98215cc03475;rule_math = pvzq3r06hi'}

res = requests.get('https://book.douban.com/top250',headers = headers)
html = etree.HTML(res.text)
result  = etree.tostring(html)
print(result)

使用LXML库解析网页数据，etree.HTML()把网页数据解析为元素对象。etree.tostring()将对象转换为字符串输出。