Selenium series 5-xpath path expression

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Xpath Introduce

• XPath Using path expressions in XML Navigation in the document
  • XPath Use path expressions to select XML A node or set of nodes in a document . These path expressions are very similar to those we see in regular computer file systems .
• XPath Contains a library of standard functions
  • XPath Contains more than 100 Built in functions . These functions are used for string values 、 The number 、 Date and time comparison 、 Nodes and QName Handle 、 Sequence processing 、 Logical values and so on .
• XPath yes XSLT The main element in
  • XPath yes XSLT The main elements of the standard . without XPath Knowledge of , You can't create XSLT file . Can be in 《XSLT course 》 Read more in . XQuery and XPointer All constructed in XPath Above the expression .XQuery 1.0 and XPath 2.0 Share the same data model , And support the same functions and operators . Can be in 《XQuery course 》 Read more about XQuery Knowledge .
• XPath It's a W3C standard
  • XPath On 1999 year 11 month 16 Japan Become W3C standard . XPath Designed for XSLT、XPointer And other things XML Parsing software uses . Can be in 《W3C The official tutorial 》 Read more about XPath Standard information

Xpath And HTML contrast

• XML Extensible markup language , Is a subset of the standard General Markup Language ; And HTML similar , But it's not HTML substitute , They are designed for different purposes .
• HTML Designed to display data , The focus is on the appearance of the data .XML Designed to transmit and store data , The focus is on the content of the data .

Xpath The term

node

stay XPath in , There are seven types of nodes ： Elements 、 attribute 、 Text 、 Namespace 、 A processing instruction 、 Comments and documentation （ root ） node .XML Documents are treated as node trees . The root of the tree is called the document node or the root node .

Please look at this XML file ：

<?xml version="1.0" encoding="UTF-8"?>

<bookstore>
  <book>
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
</bookstore>

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above XML Examples of nodes in the document ：

<bookstore> （ Document nodes ）
<author>J K. Rowling</author> （ Element nodes ）
lang="en" （ Attribute node ） 

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Basic value （ Or atomic value ,Atomic value）

The base value is a node without parent or child

above XML Examples of basic values in the document ：

J K. Rowling
"en"

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Xpath Node relationship

Father （Parent）

Every element and attribute has a parent .

In the following example ,book The element is title、author、year as well as price The father of the element ：

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

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Son （Children）

Element nodes can have zero 、 One or more children .

In the following example ,title、author、year as well as price The elements are book The child of the element ：

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

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Compatriot （Sibling）

Nodes with the same parent

In the following example ,title、author、year as well as price All elements are compatriots ：

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

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Forefathers （Ancestor）

The parent of a node 、 Father's father , wait .

In the following example ,title The ancestor of elements is book Elements and bookstore Elements ：

<bookstore>

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

</bookstore>

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Progeny （Descendant）

The child of a node , Son of son , wait .

In the following example ,bookstore The offspring of book、title、author、year as well as price Elements ：

<bookstore>

<book>
 <title>Harry Potter</title>
 <author>J K. Rowling</author>
 <year>2005</year>
 <price>29.99</price>
</book>

</bookstore>

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Xpath grammar

XPath Use path expressions to select XML A node or set of nodes in a document . Nodes are created by following paths (path) Or step (steps) To select .

XML Example

<?xml version="1.0" encoding="UTF-8"?>
 
<bookstore>
 
<book>
  <title lang="eng">Harry Potter</title>
  <price>29.99</price>
</book>
 
<book>
  <title lang="eng">Learning XML</title>
  <price>39.95</price>
</book>
 
</bookstore>

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Select node

XPath Using path expressions in XML Select node in document . The node is either by following the path or step To select . The most useful path expressions are listed below ：

expression	describe
nodename	Select all children of this node
/	Select from root node （ Take the child node ）
//	Select the node in the document from the current node that matches the selection , Regardless of their location （ Take the descendant node ）
.	Select the current node
..	Select the parent of the current node
@	Select Properties

In the table below , Some path expressions and the results of the expressions are listed ：

Path expression	result
bookstore	selection bookstore All children of the element
/bookstore	Select the root element bookstore. notes ： If the path starts with a forward slash ( / ), This path always represents the absolute path to an element ！
bookstore/book	Choose to belong to bookstore All of the child elements of book Elements
//book	Select all book Subelement , Regardless of where they are in the document
bookstore//book	Choose to belong to bookstore All of the descendants of the element book Elements , No matter where they are bookstore What's down there
//@lang	Choose the name lang All attributes of

Predicate （Predicates）

Predicate is used to find a specific node or a node containing a specified value .

The predicate is embedded in square brackets .

In the table below , Lists some path expressions with predicates , And the result of the expression ：

Path expression	result
/bookstore/book[1]	Choose to belong to bookstore The first of the child elements book Elements .
/bookstore/book[last()]	Choose to belong to bookstore The last of the child elements book Elements .
/bookstore/book[last()-1]	Choose to belong to bookstore The penultimate of a child element book Elements .
/bookstore/book[position()<4]	Select the first three that belong to bookstore Of a child element book Elements .
//title[@lang]	Select all owners named lang Property of title Elements .
//title[@lang=’eng’]	Select all title Elements , And these elements have a value of eng Of lang attribute .
/bookstore/book[price>35.00]	selection bookstore All of the elements book Elements , And one of them price The value of the element must be greater than 35.00.
/bookstore/book[price>35.00]//title	selection bookstore In the element book All of the elements title Elements , And one of them price The value of the element must be greater than 35.00.

Select unknown node

XPath Wildcards can be used to select unknown XML Elements .

wildcard	describe
*	Match any element node .
@*	Match any attribute node .
node()	Match any type of node .

In the table below , Lists some path expressions , And the results of these expressions ：

Path expression	result
/bookstore/*	selection bookstore All child elements of the element .
//*	Select all elements in the document .
//title[@*]	Select all of the title Elements .

Select several paths

By using in a path expression ”|” Operator , You can choose several paths .

In the table below , Lists some path expressions , And the results of these expressions ：

Path expression	result
//book/title | //book/price	selection book All of the elements title and price Elements .
//title | //price	Select all... In the document title and price Elements .
/bookstore/book/title | //price	Choose to belong to bookstore Elemental book All of the elements title Elements , And all the price Elements .

Reference resources

https://www.runoob.com/xpath/xpath-tutorial.html

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