This article addresses: https://www.jianshu.com/p/90e4b83575e2
XPath is a finding information in an XML document language. XPath is used to navigate through elements and attributes in an XML document.
Compared to BeautifulSoup,
installation
In Python library has provided many Xpathfeatures, but the basic or lxmlthe library, maximum efficiency. Before BeautifulSoupchapters we have introduced to lxmlhow to install.
pip install lxml
grammar
XPath uses path expressions to select nodes in an XML document. Along the path through the node, or to select a step.
We will be demonstrated with the following HTML document:
html_doc = '''<html>
<head></head>
<body>
<bookstore>
<book category="COOKING">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>
<book category="CHILDREN">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="WEB">
<title lang="en">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<price>49.99</price>
</book>
<book category="WEB">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>
</body>
</html>'''
from lxml import etree
page = etree.HTML(html_doc)
路径查找
| 表达式 | 描述 |
|---|---|
| nodename | 选取此节点的子节点。 |
| / | 从根节点选取。 |
| // | 从匹配选择的当前节点选择文档中的节点，而不考虑它们的位置。 |
| . | 选取当前节点。 |
| .. | 选取当前节点的父节点。 |
| @ | 选取属性。 |
-
查找当前节点的子节点
In [1]: page.xpath('head')
Out[1]: [<Element head at 0x111c74c48>] -
从根节点进行查找
In [2]: page.xpath('/html')
Out[2]: [<Element html at 0x11208be88>] -
从整个文档中所有节点查找
In [3]: page.xpath('//book')
Out[3]:
[<Element book at 0x1128c02c8>,
<Element book at 0x111c74108>,
<Element book at 0x111fd2288>,
<Element book at 0x1128da348>] -
选取当前节点的父节点
In [4]: page.xpath('//book')[0].xpath('..')
Out[4]: [<Element bookstore at 0x1128c0ac8>] -
选取属性
In [5]: page.xpath('//book')[0].xpath('@category')
Out[5]: ['COOKING']
节点查找
| 表达式 | 结果 |
|---|---|
| nodename[1] | 选取第一个元素。 |
| nodename[last()] | 选取最后一个元素。 |
| nodename[last()-1] | 选取倒数第二个元素。 |
| nodename[position()<3] | 选取前两个子元素。 |
| nodename[@lang] | 选取拥有名为 lang 的属性的元素。 |
| nodename[@lang='eng'] | 选取拥有lang属性，且值为 eng 的元素。 |
-
选取第二个book元素
In [1]: page.xpath('//book[2]/@category') Out[1]: ['CHILDREN'] -
选取倒数第三个book元素
In [2]: page.xpath('//book[last()-2]/@category') Out[2]: ['CHILDREN'] -
选取第二个元素开始的所有元素
In [3]: page.xpath('//book[position() > 1]/@category') Out[3]: ['CHILDREN', 'WEB', 'WEB'] -
选取category属性为WEB的的元素
In [4]: page.xpath('//book[@category="WEB"]/@category') Out[4]: ['WEB', 'WEB']
未知节点
| 通配符 | 描述 |
|---|---|
| * | 匹配任何元素节点。 |
| @* | 匹配任何属性节点。 |
-
匹配第一个book元素下的所有元素
In [1]: page.xpath('//book[1]/*') Out[1]: [<Element title at 0x111f76788>, <Element author at 0x111f76188>, <Element year at 0x1128c1a88>, <Element price at 0x1128c1cc8>]
获取节点中的文本
-
用
text()获取某个节点下的文本In [1]: page.xpath('//book[1]/author/text()') Out[1]: ['Giada De Laurentiis']如果这个节点下有多个文本，则只能取到一段。
-
用
string()获取某个节点下所有的文本In [2]: page.xpath('string(//book[1])') Out[2]: '\n Everyday Italian\n Giada De Laurentiis\n 2005\n 30.00\n '
选取多个路径
通过在路径表达式中使用“|”运算符，您可以选取若干个路径。
In [1]: page.xpath('//book[1]/title/text() | //book[1]/author/text()')
Out[1]: ['Everyday Italian', 'Giada De Laurentiis']