python爬蟲之xpath的基本使用

時間 2019-11-10

原文原文鏈接

1、簡介html

　　XPath 是一門在 XML 文檔中查找信息的語言。XPath 可用來在 XML 文檔中對元素和屬性進行遍歷。XPath 是 W3C XSLT 標準的主要元素，而且 XQuery 和 XPointer 都構建於 XPath 表達之上。python

　　參照scrapy

2、安裝ide

pip3 install lxml

3、使用ui

　　一、導入url

from lxml import etree

　　二、基本使用spa

from lxml import etree

wb_data = """
        <div>
            <ul>
                 <li class="item-0"><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(wb_data)
print(html)
result = etree.tostring(html)
print(result.decode("utf-8"))

　　從下面的結果來看，咱們打印機html其實就是一個python對象，etree.tostring(html)則是不全裏html的基本寫法，補全了缺胳膊少腿的標籤。code

<Element html at 0x39e58f0>
<html><body><div>
            <ul>
                 <li class="item-0"><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>

　　三、獲取某個標籤的內容(基本使用)，注意，獲取a標籤的全部內容，a後面就不用再加正斜槓，不然報錯。xml

　　寫法一htm

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（直接在須要查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/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

　　四、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('//*')
#打印是一個列表，須要遍歷
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)

打印：
<div>
     <ul>
         <li class="item-0"><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>

　　五、打印指定路徑下a標籤的屬性（能夠經過遍歷拿到某個屬性的值，查找標籤的內容）

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

　　六、咱們知道咱們使用xpath拿到得都是一個個的ElementTree對象，因此若是須要查找內容的話，還須要遍歷拿到數據的列表。

　　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/div/ul/li/a[@href="link2.html"]/text()')
print(html_data)
for i in html_data:
    print(i)

打印：
['second item']
second item

　　七、上面咱們找到所有都是絕對路徑（每個都是從根開始查找），下面咱們查找相對路徑，例如，查找全部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)

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

　　八、上面咱們使用絕對路徑，查找了全部a標籤的屬性等於href屬性值，利用的是/---絕對路徑，下面咱們使用相對路徑，查找一下l相對路徑下li標籤下的a標籤下的href屬性的值，注意，a標籤後面須要雙//。

html = etree.HTML(wb_data)
html_data = html.xpath('//li/a//@href')
print(html_data)
for i in html_data:
    print(i)

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

　　九、相對路徑下跟絕對路徑下查特定屬性的方法相似，也能夠說相同。

html = etree.HTML(wb_data)
html_data = html.xpath('//li/a[@href="link2.html"]')
print(html_data)
for i in html_data:
    print(i.text)

打印：
[<Element a at 0x216e468>]
second item

　　十、查找最後一個li標籤裏的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)

打印：
['fifth item']
fifth item

　　十一、查找倒數第二個li標籤裏的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)

打印：
['fourth item']
fourth item

　　十二、若是在提取某個頁面的某個標籤的xpath路徑的話，能夠以下圖：

　　//*[@id="kw"]

　　解釋：使用相對路徑查找全部的標籤，屬性id等於kw的標籤。

#!/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">first item</a></li>
            <li class="item-0"><a id='i2' href="llink.html">first item</a></li>
            <li class="item-1"><a href="llink2.html">second item<span>vv</span></a></li>
        </ul>
        <div><a href="llink2.html">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"][@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)