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python爬蟲之xpath的基本使用詳解

 更新時(shí)間：2018年04月18日 10:52:14   作者：Charles.L  
本篇文章主要介紹了python爬蟲之xpath的基本使用詳解，小編覺得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過來看看吧

一、簡介

XPath 是一門在 XML 文檔中查找信息的語言。XPath 可用來在 XML 文檔中對(duì)元素和屬性進(jìn)行遍歷。XPath 是 W3C XSLT 標(biāo)準(zhǔn)的主要元素，并且 XQuery 和 XPointer 都構(gòu)建于 XPath 表達(dá)之上。 

二、安裝

pip3 install lxml

三、使用

1、導(dǎo)入

from lxml import etree

2、基本使用

from lxml import etree
wb_data = """
    <div>
      <ul>
         <li class="item-0"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

         <li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>

         <li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

         <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

         <li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
       </ul>
     </div>

    """
html = etree.HTML(wb_data)
print(html)
result = etree.tostring(html)
print(result.decode("utf-8"))

從下面的結(jié)果來看，我們打印機(jī)html其實(shí)就是一個(gè)python對(duì)象，etree.tostring(html)則是不全里html的基本寫法，補(bǔ)全了缺胳膊少腿的標(biāo)簽。

 <Element html at 0x39e58f0>
<html><body><div>
      <ul>
         <li class="item-0"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

         <li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>

         <li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

         <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

         <li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>

       </li></ul>
     </div>
    </body></html>

3、獲取某個(gè)標(biāo)簽的內(nèi)容(基本使用)，注意，獲取a標(biāo)簽的所有內(nèi)容，a后面就不用再加正斜杠，否則報(bào)錯(cuò)。

寫法一

html = etree.HTML(wb_data)

html_data = html.xpath('/html/body/div/ul/li/a')

print(html)

for i in html_data:

  print(i.text)

<Element html at 0x12fe4b8>

first item

second item

third item

fourth item

fifth item

寫法二（直接在需要查找內(nèi)容的標(biāo)簽后面加一個(gè)/text()就行）

html = etree.HTML(wb_data)

html_data = html.xpath('/html/body/div/ul/li/a/text()')

print(html)

for i in html_data:

  print(i) 

<Element html at 0x138e4b8>

first item

second item

third item

fourth item

fifth item

4、打開讀取html文件

#使用parse打開html的文件

html = etree.parse('test.html')

html_data = html.xpath('//*')<br>#打印是一個(gè)列表，需要遍歷

print(html_data)

for i in html_data:

  print(i.text) 

html = etree.parse('test.html')

html_data = etree.tostring(html,pretty_print=True)

res = html_data.decode('utf-8')

print(res)

 

打?。?

<div>

   <ul>

     <li class="item-0"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

     <li class="item-1"><a href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>

     <li class="item-inactive"><a href="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

     <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

     <li class="item-0"><a href="link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a></li>

   </ul>

</div>

5、打印指定路徑下a標(biāo)簽的屬性（可以通過遍歷拿到某個(gè)屬性的值，查找標(biāo)簽的內(nèi)容）

html = etree.HTML(wb_data)

html_data = html.xpath('/html/body/div/ul/li/a/@href')

for i in html_data:

  print(i)

打印：

link1.html

link2.html

link3.html

link4.html

link5.html

6、我們知道我們使用xpath拿到得都是一個(gè)個(gè)的ElementTree對(duì)象，所以如果需要查找內(nèi)容的話，還需要遍歷拿到數(shù)據(jù)的列表。

查到絕對(duì)路徑下a標(biāo)簽屬性等于link2.html的內(nèi)容。

html = etree.HTML(wb_data)

html_data = html.xpath('/html/body/div/ul/li/a[@href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]/text()')

print(html_data)

for i in html_data:

  print(i)

打印：

['second item']

second item

7、上面我們找到全部都是絕對(duì)路徑（每一個(gè)都是從根開始查找），下面我們查找相對(duì)路徑，例如，查找所有l(wèi)i標(biāo)簽下的a標(biāo)簽內(nèi)容。

html = etree.HTML(wb_data)

html_data = html.xpath('//li/a/text()')

print(html_data)

for i in html_data:

  print(i)

打?。?/p>

['first item', 'second item', 'third item', 'fourth item', 'fifth item']

first item

second item

third item

fourth item

fifth item

8、上面我們使用絕對(duì)路徑，查找了所有a標(biāo)簽的屬性等于href屬性值，利用的是/---絕對(duì)路徑，下面我們使用相對(duì)路徑，查找一下l相對(duì)路徑下li標(biāo)簽下的a標(biāo)簽下的href屬性的值，注意，a標(biāo)簽后面需要雙//。

html = etree.HTML(wb_data)

html_data = html.xpath('//li/a//@href')

print(html_data)

for i in html_data:

  print(i)

打?。?/p>

['link1.html', 'link2.html', 'link3.html', 'link4.html', 'link5.html']

link1.html

link2.html

link3.html

link4.html

link5.html

9、相對(duì)路徑下跟絕對(duì)路徑下查特定屬性的方法類似，也可以說相同。

html = etree.HTML(wb_data)

html_data = html.xpath('//li/a[@href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]')

print(html_data)

for i in html_data:

  print(i.text)

打印：

[<Element a at 0x216e468>]

second item

10、查找最后一個(gè)li標(biāo)簽里的a標(biāo)簽的href屬性

html = etree.HTML(wb_data)

html_data = html.xpath('//li[last()]/a/text()')

print(html_data)

for i in html_data:

  print(i)

打?。?/p>

['fifth item']

fifth item

11、查找倒數(shù)第二個(gè)li標(biāo)簽里的a標(biāo)簽的href屬性 

html = etree.HTML(wb_data)

html_data = html.xpath('//li[last()-1]/a/text()')

print(html_data)

for i in html_data:

  print(i)

打印：

['fourth item']

fourth item

12、如果在提取某個(gè)頁面的某個(gè)標(biāo)簽的xpath路徑的話，可以如下圖：

//*[@id="kw"]

解釋：使用相對(duì)路徑查找所有的標(biāo)簽，屬性id等于kw的標(biāo)簽。

常用

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from scrapy.selector import Selector, HtmlXPathSelector
from scrapy.http import HtmlResponse
html = """<!DOCTYPE html>
<html>
  <head lang="en">
    <meta charset="UTF-8">
    <title></title>
  </head>
  <body>
    <ul>
      <li class="item-"><a id='i1' href="link.html" rel="external nofollow" rel="external nofollow" >first item</a></li>
      <li class="item-0"><a id='i2' href="llink.html" rel="external nofollow" >first item</a></li>
      <li class="item-1"><a href="llink2.html" rel="external nofollow" rel="external nofollow" >second item<span>vv</span></a></li>
    </ul>
    <div><a href="llink2.html" rel="external nofollow" rel="external nofollow" >second item</a></div>
  </body>
</html>
"""
response = HtmlResponse(url='http://example.com', body=html,encoding='utf-8')
# hxs = HtmlXPathSelector(response)
# print(hxs)
# hxs = Selector(response=response).xpath('//a')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[2]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[@id]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[@id="i1"]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[@href="link.html" rel="external nofollow" rel="external nofollow" ][@id="i1"]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[contains(@href, "link")]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[starts-with(@href, "link")]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]/text()').extract()
# print(hxs)
# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]/@href').extract()
# print(hxs)
# hxs = Selector(response=response).xpath('/html/body/ul/li/a/@href').extract()
# print(hxs)
# hxs = Selector(response=response).xpath('//body/ul/li/a/@href').extract_first()
# print(hxs)
 
# ul_list = Selector(response=response).xpath('//body/ul/li')
# for item in ul_list:
#   v = item.xpath('./a/span')
#   # 或
#   # v = item.xpath('a/span')
#   # 或
#   # v = item.xpath('*/a/span')
#   print(v)

以上就是本文的全部內(nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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