一、簡介
XPath 是一門在 XML 文檔中尋找資訊的語言。XPath 可用來在 XML 文檔中對元素和屬性進行遍曆。XPath 是 W3C XSLT 標準的主要元素，並且 XQuery 和 XPointer 都構建於 XPath 表達之上。
二、安裝
pip3 install lxml
三、使用
1、匯入
from lxml import etree
2、基本使用
from lxml import etreewb_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"))
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>
3、擷取某個標籤的內容(基本使用)，注意，擷取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('/html/body/p/ul/li/a')print(html)for i in html_data: print(i.text)<Element html at 0x12fe4b8>first itemsecond itemthird itemfourth itemfifth item
寫法二（直接在需要尋找內容的標籤後面加一個/text()就行）
html = etree.HTML(wb_data)html_data = html.xpath('/html/body/p/ul/li/a/text()')print(html)for i in html_data: print(i) <Element html at 0x138e4b8>first itemsecond itemthird itemfourth itemfifth item
4、開啟讀取html檔案
#使用parse開啟html的檔案html = etree.parse('test.html')html_data = html.xpath('//*')<br>#列印是一個列表，需要遍曆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) 列印：<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>
5、列印指定路徑下a標籤的屬性（可以通過遍曆拿到某個屬性的值，尋找標籤的內容）
html = etree.HTML(wb_data)html_data = html.xpath('/html/body/p/ul/li/a/@href')for i in html_data: print(i)
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，所以如果需要尋找內容的話，還需要遍曆拿到資料的列表。
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('/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()')print(html_data)for i in html_data: print(i)
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尋找），下面我們尋找相對路徑，例如，尋找所有li標籤下的a標籤內容。
html = etree.HTML(wb_data)html_data = html.xpath('//li/a/text()')print(html_data)for i in html_data: print(i)
列印：
['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，尋找了所有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，尋找一下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('//li/a//@href')print(html_data)for i in html_data: print(i)
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('//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)
列印：
[<Element a at 0x216e468>]
second item
10、尋找最後一個li標籤裡的a標籤的href屬性
html = etree.HTML(wb_data)html_data = html.xpath('//li[last()]/a/text()')print(html_data)for i in html_data: print(i)
列印：
['fifth item']
fifth item
11、尋找倒數第二個li標籤裡的a標籤的href屬性
html = etree.HTML(wb_data)html_data = html.xpath('//li[last()-1]/a/text()')print(html_data)for i in html_data: print(i)
列印：
['fourth item']
fourth item
12、如果在提取某個頁面的某個標籤的xpath路徑的話，可以如：
//*[@id="kw"]
解釋：使用相對路徑尋找所有的標籤，屬性id等於kw的標籤。
常用
#!/usr/bin/env python# -*- coding:utf-8 -*-from scrapy.selector import Selector, HtmlXPathSelectorfrom scrapy.http import HtmlResponsehtml = """<!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> <p><a href="llink2.html" rel="external nofollow" rel="external nofollow" >second item</a></p> </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)
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