captcha是Completely Automated Public Turing Test to Tell Computers and Humans Apart ，全自动区分计算机和人类的图灵测试)的简称。

登陆失败若干次之后，豆瓣登录页面才会出现验证码。所以为了确保py文件运行正确，要先故意输错几次，出现验证码框之后，再运行。：)

使用Python3.6。

from urllib.request import urlretrieve
import requests
from bs4 import BeautifulSoup
from os import remove
try:
    import cookielib
except:
    import http.cookiejar as cookielib
try:
    from PIL import Image
except:
    pass

url = 'https://accounts.douban.com/login'

datas = {'source': 'index_nav',
         'remember': 'on'}

headers = {'Referer': 'https://www.douban.com/',
           'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36'
           ' (KHTML, like Gecko) Chrome/60.0.3112.101 Safari/537.36',
           'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
           'Accept-Language': 'zh-CN,zh;q=0.8'}

# 尝试使用cookie信息
session = requests.session()
session.cookies = cookielib.LWPCookieJar(filename='cookies')
try:
    session.cookies.load(ignore_discard=True)
except:
    print("Cookies未能加载")
    #cookies加载不成功，则输入账号密码信息
    datas['form_email'] = input('Please input your account:')
    datas['form_password'] = input('Please input your password:')


def get_captcha():
    '''
    获取验证码及其ID
    '''
    r = requests.post(url, data=datas, headers=headers)
    page = r.text
    soup = BeautifulSoup(page, "html.parser")
    # 利用bs4获得验证码图片地址
    img_src = soup.find('img', {'id': 'captcha_image'}).get('src')
    urlretrieve(img_src, 'captcha.jpg')
    try:
        im = Image.open('captcha.jpg')
        im.show()
        im.close()
    except:
        print('到本地目录打开captcha.jpg获取验证码')
    finally:
        captcha = input('please input the captcha:')
        remove('captcha.jpg')
    captcha_id = soup.find(
        'input', {'type': 'hidden', 'name': 'captcha-id'}).get('value')
    return captcha, captcha_id


def isLogin():
    '''
    通过查看用户个人账户信息来判断是否已经登录
    '''
    url = "https://www.douban.com/accounts/"
    login_code = session.get(url, headers=headers,
                             allow_redirects=False).status_code
    if login_code == 200:
        return True
    else:
        return False


def login():
    captcha, captcha_id = get_captcha()
    # 增加表数据
    datas['captcha-solution'] = captcha
    datas['captcha-id'] = captcha_id
    login_page = session.post(url, data=datas, headers=headers)
    page = login_page.text
    soup = BeautifulSoup(page, "html.parser")
    result = soup.findAll('div', attrs={'class': 'title'})
    #进入豆瓣登陆后页面，打印热门内容
    for item in result:
        print(item.find('a').get_text())
    # 保存 cookies 到文件，
    # 下次可以使用 cookie 直接登录，不需要输入账号和密码
    session.cookies.save()

if __name__ == '__main__':
    if isLogin():
        print('Login successfully')
    else:
        login()

将标题抓取下来了！