The use of 13_python_ analytic library _xpath

Directory

• 1. Installing Xpath
• 2, XPath basic use
• 3. XPath syntax
  • 3.1. Commonly used path expressions
  • 3.2. Finding specific elements based on predicates
  • 3.3. Wildcard characters
  • 3.4. Select multiple paths

1. Installing Xpath

pip install lxml

2, XPath basic use

from lxml import etreehtml = ‘‘‘<p class="drink">饮料套餐    <a class="drink" id="coffee">咖啡</a>     <a class="drink" id="milk">牛奶</a></p>‘‘‘selector = etree.HTML(html)content = selector.xpath(‘//a[@id="coffee"]/text()‘)print(content)

3. XPath syntax 3.1, commonly used path expressions

An expression	Description
NodeName	Select all child nodes of this node.
/	Select from the root node.
//	Selects the nodes in the document from the current node that matches the selection, regardless of their location.
.	Select the current node.
..	Selects the parent node of the current node.
@	Select the attribute.

• Instance

Path Expression	Results
Bookstore	Selects all child nodes of the bookstore element.
/bookstore	Select the root element bookstore. Note: If the path starts with a forward slash (/), this path always represents the absolute path to an element!
Bookstore/book	Selects all book elements that belong to a child element of bookstore.
Book	Selects all book child elements, regardless of their position in the document.
Bookstore//book	Selects all book elements that belong to descendants of the bookstore element, regardless of where they are located under bookstore.
@lang	Select all attributes that are named Lang.

3.2. Finding specific elements based on predicates

Path Expression	Results
/BOOKSTORE/BOOK[1]	Selects the first book element that belongs to a bookstore child element.
/bookstore/book[last ()]	Select the last book element that belongs to the bookstore child element.
/bookstore/book[last ()-1]	Select the second-to-last book element that belongs to the bookstore child element.
/bookstore/book[position () <3]	Select the first two book element that belongs to the child element of the bookstore element.
title[@lang]	Select all the title elements that have properties named Lang.
title[@lang = ' Eng ']	Selects all title elements, and these elements have the lang attribute value of Eng.
/BOOKSTORE/BOOK[PRICE>35.00]	Selects all the book elements of the bookstore element, and the value of the price element must be greater than 35.00.
/bookstore/book[price>35.00]/title	Selects all the title elements of the book element in the bookstore element, and the value of the price element must be greater than 35.00.

3.3. Wildcard characters

wildcard characters	Description
*	Matches any element node.
@*	matches any attribute node.
Node ()	Matches any type of node.

• Instance

Path Expression	Results
/bookstore/*	Selects all child elements of the bookstore element.
//*	Selects all elements in the document.
Title[@*]	Select all the title elements with attributes.

3.4. Select multiple paths

• By using the ' | ' in a path expression operator, you can select a number of paths.

Path Expression	Results
Book/title | Book/price	Selects all the title and price elements of the book element.
Title | Price	Selects all the title and price elements in the document.
/bookstore/book/title | Price	Selects all the title elements of the book element that belong to the bookstore element, and all the price elements in the document.

Resources:

W3school's XPath tutorial

The use of 13_python_ analytic library _xpath