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python爬蟲之xpath的基本使用詳解

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Apr 27, 2018 am 11:01 AM

python xpath 使用

這篇文章主要介紹了python爬蟲之xpath的基本使用詳解，現在分享給大家，也給大家做個參考。一起來看看吧

一、簡介

#XPath 是一種在 XML 文件中尋找資訊的語言。 XPath 可用於在 XML 文件中對元素和屬性進行遍歷。 XPath 是 W3C XSLT 標準的主要元素，而 XQuery 和 XPointer 都建構在 XPath 表達之上。

二、安裝

pip3 install lxml

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三、使用

1、導入

from lxml import etree

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2、基本使用

from lxml import etree
wb_data = """
    <p>
      <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>
     </p>

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

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從下面的結果來看，我們印表機html其實就是一個python對象，etree.tostring(html)則是不全裡html的基本寫法，補全了缺胳膊少腿的標籤。

 <Element html at 0x39e58f0>
<html><body><p>
      <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>
     </p>
    </body></html>

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3、取得某個標籤的內容(基本使用)，注意，取得a標籤的所有內容，a後面就不用再加正斜杠，否則報錯。

寫法一

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;/html/body/p/ul/li/a&#39;)

print(html)

for i in html_data:

  print(i.text)

<Element html at 0x12fe4b8>

first item

second item

third item

fourth item

fifth item

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#寫法二（直接在需要尋找內容的標籤後面加上一個/text()就行）

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;/html/body/p/ul/li/a/text()&#39;)

print(html)

for i in html_data:

  print(i) 

<Element html at 0x138e4b8>

first item

second item

third item

fourth item

fifth item

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4、開啟讀取html檔案

#使用parse打开html的文件

html = etree.parse(&#39;test.html&#39;)

html_data = html.xpath(&#39;//*&#39;)<br>#打印是一个列表，需要遍历

print(html_data)

for i in html_data:

  print(i.text)

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html = etree.parse(&#39;test.html&#39;)

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

res = html_data.decode(&#39;utf-8&#39;)

print(res)

 

打印：

<p>

   <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>

</p>

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5、列印指定路徑下a標籤的屬性（可以透過遍歷拿到某個屬性的值，找出標籤的內容）

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;/html/body/p/ul/li/a/@href&#39;)

for i in html_data:

  print(i)

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列印：

link1.html
link2.html
link3.html
link4.html
link5.html

6、我們知道我們使用xpath拿到得都是一個個的ElementTree對象，所以如果需要找內容的話，還需要遍歷拿到資料的列表。

查到絕對路徑下a標籤屬性等於link2.html的內容。

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;/html/body/p/ul/li/a[@href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]/text()&#39;)

print(html_data)

for i in html_data:

  print(i)

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列印：

#['second item']
second item

#7、上面我們找到全部都是絕對路徑（每一個都是從根開始查找），下面我們查找相對路徑，例如，查找所有li標籤下的a標籤內容。

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;//li/a/text()&#39;)

print(html_data)

for i in html_data:

  print(i)

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印刷：

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

8、上面我們使用絕對路徑，查找了所有a標籤的屬性等於href屬性值，利用的是/---絕對路徑，下面我們使用相對路徑，查找l相對路徑下li標籤下的a標籤下的href屬性的值，注意，a標籤後面需要雙//。

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;//li/a//@href&#39;)

print(html_data)

for i in html_data:

  print(i)

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列印：

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

9、相對路徑下跟絕對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(&#39;//li/a[@href="link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]&#39;)

print(html_data)

for i in html_data:

  print(i.text)

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列印：

[]
#second item

10、找出最後一個li標籤裡的a標籤的href屬性

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;//li[last()]/a/text()&#39;)

print(html_data)

for i in html_data:

  print(i)

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列印：

['fifth item']
fifth item

11、找出倒數第二個li標籤裡的a標籤的href屬性

html = etree.HTML(wb_data)

html_data = html.xpath(&#39;//li[last()-1]/a/text()&#39;)

print(html_data)

for i in html_data:

  print(i)

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列印：

['fourth item']
fourth item

12、如果在擷取某個頁面的某個標籤的xpath路徑的話，可以如下圖：

//*[@id="kw"]

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解釋：使用相對路徑來尋找所有的標籤，屬性id等於kw的標籤。

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=&#39;i1&#39; href="link.html" rel="external nofollow" rel="external nofollow" >first item</a></li>
      <li class="item-0"><a id=&#39;i2&#39; 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>
    <p><a href="llink2.html" rel="external nofollow" rel="external nofollow" >second item</a></p>
  </body>
</html>
"""
response = HtmlResponse(url=&#39;http://example.com&#39;, body=html,encoding=&#39;utf-8&#39;)
# hxs = HtmlXPathSelector(response)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[2]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[@id]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[@id="i1"]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[@href="link.html" rel="external nofollow" rel="external nofollow" ][@id="i1"]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[contains(@href, "link")]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[starts-with(@href, "link")]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[re:test(@id, "i\d+")]&#39;)
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[re:test(@id, "i\d+")]/text()&#39;).extract()
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//a[re:test(@id, "i\d+")]/@href&#39;).extract()
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;/html/body/ul/li/a/@href&#39;).extract()
# print(hxs)
# hxs = Selector(response=response).xpath(&#39;//body/ul/li/a/@href&#39;).extract_first()
# print(hxs)
 
# ul_list = Selector(response=response).xpath(&#39;//body/ul/li&#39;)
# for item in ul_list:
#   v = item.xpath(&#39;./a/span&#39;)
#   # 或
#   # v = item.xpath(&#39;a/span&#39;)
#   # 或
#   # v = item.xpath(&#39;*/a/span&#39;)
#   print(v)

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