python中lxml模块的使用

lxml是python的一个解析库，支持HTML和XML的解析，支持XPath解析方式，而且解析效率非常高

1.lxml的安装

pip install lxml

2.导入lxml 的 etree 库

 from lxml import etree

3.利用etree.HTML，将字符串转化为Element对象,Element对象具有xpath的方法,返回结果的列表，能够接受bytes类型的数据和str类型的数据。

from lxml import etree
html = etree.HTML(response.text)
ret_list = html.xpath("xpath字符串")

也可以这样使用：

from lxml import etree
htmlDiv = etree.HTML(response.content.decode())
hrefs = htmlDiv.xpath("//h4//a/@href")

4.把转化后的element对象转化为字符串，返回bytes类型，etree.tostring(element)

假设我们现有如下的html字符换，尝试对他进行操作:

<div> <ul>
<li class="item-1"><a href="link1.html">first item</a></li>
<li class="item-1"><a href="link2.html">second item</a></li>
<li class="item-inactive"><a href="link3.html">third item</a></li>
<li class="item-1"><a href="link4.html">fourth item</a></li>
<li class="item-0"><a href="link5.html">fifth item</a> # 注意，此处缺少一个 </li> 闭合标签
</ul> </div>

代码示例：

from lxml import etree
text = ''' <div> <ul> <li class="item-1"><a href="link1.html">first item</a></li> <li class="item-1"><a href="link2.html">second item</a></li> <li class="item-inactive"><a href="link3.html">third item</a></li> <li class="item-1"><a href="link4.html">fourth item</a></li> <li class="item-0"><a href="link5.html">fifth item</a> </ul> </div> '''html = etree.HTML(text)
print(type(html)) handeled_html_str = etree.tostring(html).decode()
print(handeled_html_str)

输出结果：

<class 'lxml.etree._Element'>
<html><body><div> <ul> <li class="item-1"><a href="link1.html">first item</a></li> <li class="item-1"><a href="link2.html">second item</a></li> <li class="item-inactive"><a href="link3.html">third item</a></li> <li class="item-1"><a href="link4.html">fourth item</a></li> <li class="item-0"><a href="link5.html">fifth item</a> </li></ul> </div> </body></html>

可以发现，lxml确实能够把确实的标签补充完成，但是请注意lxml是人写的，很多时候由于网页不够规范，或者是lxml的bug。
即使参考url地址对应的响应去提取数据，任然获取不到，这个时候我们需要使用etree.tostring的方法，观察etree到底把html转化成了什么样子，即根据转化后的html字符串去进行数据的提取。

5.lxml的深入练习

from lxml import etree
text = ''' <div> <ul> <li class="item-1"><a href="link1.html">first item</a></li> <li class="item-1"><a href="link2.html">second item</a></li> <li class="item-inactive"><a href="link3.html">third item</a></li> <li class="item-1"><a href="link4.html">fourth item</a></li> <li class="item-0"><a href="link5.html">fifth item</a> </ul> </div> '''html = etree.HTML(text)#获取href的列表和title的列表
href_list = html.xpath("//li[@class='item-1']/a/@href")
title_list = html.xpath("//li[@class='item-1']/a/text()")#组装成字典
for href in href_list:item = {}item["href"] = hrefitem["title"] = title_list[href_list.index(href)]print(item)

输出为：

{'href': 'link1.html', 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}

6.lxml模块的进阶使用

返回的是element对象，可以继续使用xpath方法，对此我们可以在后面的数据提取过程中：先根据某个标签进行分组，分组之后再示例如下：

from lxml import etree
text = ''' <div> <ul> <li class="item-1"><a>first item</a></li> <li class="item-1"><a href="link2.html">second item</a></li> <li class="item-inactive"><a href="link3.html">third item</a></li> <li class="item-1"><a href="link4.html">fourth item</a></li> <li class="item-0"><a href="link5.html">fifth item</a> </ul> </div> '''html = etree.HTML(text)li_list = html.xpath("//li[@class='item-1']")
print(li_list)

结果为：

[<Element li at 0x11106cb48>, <Element li at 0x11106cb88>, <Element li at 0x11106cbc8>]数据的提取

可以发现结果是一个element对象，这个对象能够继续使用xpath方法
先根据li标签进行分组，之后再进行数据的提取

from lxml import etree
text = ''' <div> <ul> <li class="item-1"><a>first item</a></li> <li class="item-1"><a href="link2.html">second item</a></li> <li class="item-inactive"><a href="link3.html">third item</a></li> <li class="item-1"><a href="link4.html">fourth item</a></li> <li class="item-0"><a href="link5.html">fifth item</a> </ul> </div> '''#根据li标签进行分组
html = etree.HTML(text)
li_list = html.xpath("//li[@class='item-1']")#在每一组中继续进行数据的提取
for li in li_list:item = {}item["href"] = li.xpath("./a/@href")[0] if len(li.xpath("./a/@href"))>0 else Noneitem["title"] = li.xpath("./a/text()")[0] if len(li.xpath("./a/text()"))>0 else Noneprint(item)

结果是：

{'href': None, 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}

7.案列：贴吧极速版：

代码如下：

import requests
from lxml import etreeclass TieBaSpider:def __init__(self, tieba_name):#1. start_urlself.start_url= "http://tieba.baidu.com/mo/q---C9E0BC1BC80AA0A7CE472600CDE9E9E3%3AFG%3D1-sz%40320_240%2C-1-3-0--2--wapp_1525330549279_782/m?kw={}&lp=6024".format(tieba_name)self.headers = {"User-Agent": "Mozilla/5.0 (Linux; Android 8.0; Pixel 2 Build/OPD3.170816.012) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Mobile Safari/537.36"}self.part_url = "http://tieba.baidu.com/mo/q---C9E0BC1BC80AA0A7CE472600CDE9E9E3%3AFG%3D1-sz%40320_240%2C-1-3-0--2--wapp_1525330549279_782"def parse_url(self,url): #发送请求，获取响应# print(url)response = requests.get(url,headers=self.headers)return response.contentdef get_content_list(self,html_str): #3. 提取数据html = etree.HTML(html_str)div_list = html.xpath("//body/div/div[contains(@class,'i')]")content_list = []for div in div_list:item = {}item["href"] = self.part_url+div.xpath("./a/@href")[0]item["title"] = div.xpath("./a/text()")[0]item["img_list"] = self.get_img_list(item["href"], [])content_list.append(item)#提取下一页的url地址next_url = html.xpath("//a[text()='下一页']/@href")next_url = self.part_url + next_url[0] if len(next_url)>0 else Nonereturn content_list, next_urldef get_img_list(self,detail_url, img_list):#1. 发送请求，获取响应detail_html_str = self.parse_url(detail_url)#2. 提取数据detail_html = etree.HTML(detail_html_str)img_list += detail_html.xpath("//img[@class='BDE_Image']/@src")#详情页下一页的url地址next_url = detail_html.xpath("//a[text()='下一页']/@href")next_url = self.part_url + next_url[0] if len(next_url)>0 else Noneif next_url is not None: #当存在详情页的下一页，请求return self.get_img_list(next_url, img_list)#else不用写img_list = [requests.utils.unquote(i).split("src=")[-1] for i in img_list]return img_listdef save_content_list(self,content_list):#保存数据for content in content_list:print(content)def run(self): #实现主要逻辑next_url = self.start_urlwhile next_url is not None:#1. start_url#2. 发送请求，获取响应html_str = self.parse_url(next_url)#3. 提取数据content_list, next_url = self.get_content_list(html_str)#4. 保存self.save_content_list(content_list)#5. 获取next_url，循环2-5if __name__ == '__main__':tieba = TieBaSpider("每日中国")tieba.run()