Beautifulsoup和xPath的基本使用

Beautifulsoup的基本使用

• 导包：from bs4 import BeautifulSoup

• 解析：soup1 = BeautifulSoup(html,'html.parser')，这里的html是一个字符串，一般都是response的text属性。

• find和find_all

  • find：例如tag = soup.find(name='div', attrs={"class":"tags"})，返回的是一个Tag类的标签，是满足class为tags的第一个div标签。
  • find_all:例如tag = soup.find_all(name='div', attrs={"class":"tags"})，返回的是所有满足class为tags的div标签，是一个列表。
  • name=可以省略不写，若是id属性可写为id=‘id名称’，class_=‘class名称’。

• 获得内容

  • 属性内容：例如url = a.get('href')，这里的a是一个标签
  • 文本内容：例如content = a.get_text(),a是一个标签

• select选择器：想css选择器一样定位，比上面的find_all方便一点

  • 找到所有a标签：all_a = soup.select('a')
  • 找到所有class为tags的div标签：tag = soup.select('div.tags')
  • 找到id为tag1的div标签：tag = soup.select(div#tag1)，返回的也是列表

• children：找到某标签的所有孩子标签，childs = a.children,结果是一个列表，注意列表中不一定都是Tag类，还有一些String，要去掉。一般都会判断一下：if isinstance(p,bs4.element.Tag):p是列表中的某一个元素。

xPath和lxml的基本使用

• 导包：from lxml import etree,windows下要装一个东西：pip install pypiwin32

• xPath基本语法

  • //div[@class='tag'],这样就是找到了所有class为tag的div标签

  • //div[@class='tag']/text(),获得class为tag的标签里的内容

  • //link[@href]获得link标签的href属性值

• python中使用xPath

  • 解析：dom = etree.HTML(text),text是一个字符串
  • 查找：content = dom.xpath("//span[@class='short']/text()"),返回的是一个列表
  • date = dom.xpath("//span[@class='info']/span[@class='time']/text()")这是在某父节点下找某子节点

例子：爬取豆瓣电影《阳光灿烂的日子》短评

使用Beautifulsoup爬取

from bs4 import BeautifulSoup
import requests
import csv
import time
'''
爬取电影《阳光灿烂的日子》在豆瓣上的所有短评
用beautifulsoup来做
'''


def getAllUrls(list):
    url = 'https://movie.douban.com/subject/1291875/comments?start='
    for page in range(0, 201, 20):
        list.append(url + str(page))


def getComment(url):
    headers = {
    'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) \
    AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36'
    }
    res = requests.get(url, headers=headers)
    soup = BeautifulSoup(res.text, 'html.parser')
    contentSpan = soup.select('span.short')
    content = []
    for c in contentSpan:
        content.append(c.get_text())
    userSpan = soup.select('span.comment-info')
    user = []
    date = []
    for u in userSpan:
        user.append(u.find('a').get_text())
    dateSpan = soup.select('span.comment-time ')
    date = []
    for d in dateSpan:
        date.append(d.get_text())
    infos = []
    for i in range(20):
        info = {}
        info['username'] = user[i]    
        info['content'] = content[i]    
        info['date'] = date[i] 
        infos.append(info)   
    return infos


def write2csv():
    url_list = []
    getAllUrls(url_list)
    with open('comments_by_bs4.csv', 'w', encoding='gbk', newline='', errors='ignore') as file:
        csvWriter = csv.writer(file)
        csvWriter.writerow(['用户名', '评论', '评论时间'])
        for url in url_list:
            infos = getComment(url)
            for info in infos:
                csvWriter.writerow([info['username'], info['content'], info['date'].strip()])


if __name__ == '__main__':
    start_time = time.time()
    write2csv()
    end_time = time.time()
    print(round(end_time - start_time, 2), '秒')
    

使用xPath和lxml爬取

from lxml import etree
import requests
import csv
import time
'''
爬取电影《阳光灿烂的日子》在豆瓣上的所有短评
以lxml和xPath来做
'''


def getAllUrls(list):
    url = 'https://movie.douban.com/subject/1291875/comments?start='
    for page in range(0, 201, 20):
        list.append(url + str(page))


def getComment(url):
    headers = {
    'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) \
    AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36'
    }
    res = requests.get(url, headers=headers)
    dom = etree.HTML(res.text)
    content = dom.xpath("//span[@class='short']/text()")
    user = dom.xpath("//span[@class='comment-info']/a/text()")
    date = dom.xpath("//span[@class='comment-info']/span[@class='comment-time ']/text()") 
    infos = []
    for i in range(20):
        info = {}
        info['username'] = user[i]    
        info['content'] = content[i]    
        info['date'] = date[i] 
        infos.append(info)   
    return infos


def write2csv():
    url_list = []
    getAllUrls(url_list)
    with open('comments_by_xPath.csv', 'w', encoding='gbk', newline='', errors='ignore') as file:
        csvWriter = csv.writer(file)
        csvWriter.writerow(['用户名', '评论', '评论时间'])
        for url in url_list:
            infos = getComment(url)
            for info in infos:
                csvWriter.writerow([info['username'], info['content'], info['date'].strip()])


if __name__ == '__main__':
    start_time = time.time()
    write2csv()
    end_time = time.time()
    print(round(end_time - start_time, 2), '秒')
                
    

测试了一下时间，xPath明显快一点，速度大概是Beautifulsoup的1.5倍，而且感觉xPath用起来顺手一点。