Pyhton Crawler (9)--using XPath to extract web information

1. XPath Basics 1.1 What is XPath.

XPath is a language for finding information (nodes) in an XML document . XPath can be used to traverse elements and attributes in an XML document. 1.2 node

The node is the smallest unit in which XPath extracts information from XML documents , with a total of 7 :

(1) elements node (element)

(2) property node (attribute)

(3) text node

(4) name naming node (namespace)

(5) Processing command nodes (processing-instruction)

(6) annotation node (comment)

(7) root node 1.3 node Relationship

(1) parent: Each element and attribute has a parent node.

(2) Sub-node (child): An element node can have 0, one, or more child nodes.

(3) sibling node (sibling): A node that has the same parent.

(4) predecessor node (ancestor): The parent node of a node's parent node.

(5) descendant (descendant): A child of a node's child node. 1.4 XPath Basic Usage 1.4.1 Basic Syntax:

(1)//(double slash): locates the root node , scans the Full-text, selects all eligible content in the document, and returns as a list .

(2)/(single slash): Look for the next-level path tag of the current label path or manipulate the current tab contents .

(3) /text (): Gets the text content under the current path.

(4)/@xxxx: Extract The property value of the label under the current path .

(5) | Optional: use | To select a number of paths such as //p |//div Select all eligible P and div tags under the current path.

(6). Point : Used to select the current node .

(7). (double point): Select the parent node of the current node .

(8)"*" (wildcard character): represents the matching of any element node .

(9)"@*" (wildcard character): Indicates that any property value is matched .

(Ten)"node ()" (wildcard): Represents a node that matches any type . 1.4.2 XPath extract element sample

#-*-Coding:utf-8-*-"" "Created on Tue June 10:23:19
2017

@author: Administrator" "" from

lxml i Mport etree

Text = ' ' 
 
The results of the execution are shown in the following illustration: