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Must master to improve your skills! Summary of lxml selector tips and supported selectors!

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Release： 2024-01-13 09:17:06

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Must master to improve your skills! Summary of lxml selector tips and supported selectors!

A must for advancement! Tips on using lxml selectors and a list of supported selectors!

Overview:

The selector is a very important tool when performing web data crawling or data extraction. In Python, there are many selector libraries to choose from, among which lxml is a powerful selector library. This article will introduce the usage skills of lxml selector and a list of supported selectors to help readers further improve the efficiency of data extraction.

1. Introduction to lxml selector

lxml is a Python-based parser library that provides extensible XPath selectors and CSS selectors for parsing HTML and XML documents. The main advantage of the lxml selector is that it is fast, powerful and suitable for processing large files. Before using the lxml selector, you need to install the lxml library first. You can install it through the following command:

pip install lxml

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2. Basic usage of the lxml selector

The basic usage of the lxml selector is very simple. You only need to import the corresponding module and create a selector object, and then use the selector object to extract data.

First, import the lxml library and corresponding module:

from lxml import etree

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Then, parse the HTML or XML document and create the selector object:

# 解析HTML文档
html = '''
<html>
    <body>
        <div class="container">
            <h1>标题1</h1>
            <p class="content">内容1</p>
        </div>
        <div class="container">
            <h1>标题2</h1>
            <p class="content">内容2</p>
        </div>
    </body>
</html>
'''

# 创建选择器对象
selector = etree.HTML(html)

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Next, you can use the select Container object to extract data. The lxml selector supports XPath selectors and CSS selectors. Their usage will be introduced below.

XPath Selector

XPath (XML Path Language) is a language used to navigate and extract information in XML or HTML documents. The lxml selector supports XPath selectors, through which the elements to be extracted can be accurately located.

Common XPath syntax includes:

Select elements: /, //, []
Select attributes: @
Select text: text()
Select parent node: ..

Here are a few examples of XPath selectors:

# 提取h1标签的文本
titles = selector.xpath('//h1/text()')
print(titles)  # 输出：['标题1', '标题2']

# 提取p标签的属性class值
classes = selector.xpath('//p/@class')
print(classes)  # 输出：['content', 'content']

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CSS Selector

CSS (Cascading Style Sheets) Selector Is a language for selecting elements in HTML documents. The lxml selector also supports CSS selectors, through which elements can be positioned through tags, classes, IDs, etc.

Common CSS selectors include:

Select tag: tag name
Select class:.Class name
Select ID: #ID name
Select parent-child relationship: space
Select adjacent sibling relationship:
Select subsequent Brotherhood: ~

The following are examples of several CSS selectors:

# 提取h1标签的文本
titles = selector.cssselect('h1')
for title in titles:
    print(title.text)  # 输出：标题1、标题2

# 提取p标签的属性class值
classes = selector.cssselect('p.content')
for p in classes:
    print(p.get('class'))  # 输出：content、content

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3. List of selectors supported by the lxml selector

# The selectors supported by ##lxml selector include XPath selector and CSS selector. The following are some commonly used selectors:

XPath selector:
- /: Select the root node
- //: Select all nodes
- []: Conditional selection
- @: Select attribute
- text(): Select text
- ..: Select parent node
CSS Selector:
- Class Selector:
- .Class Name
- #ID name
- Adjacent sibling relationship:
- ~

In addition to the above commonly used selectors, lxml also supports more selectors, such as position selectors , attribute selector, etc. Readers can check the official documentation of lxml for in-depth study and understanding.

Conclusion:

lxml selector is a powerful selector library that supports XPath selectors and CSS selectors and is suitable for parsing and data extraction of HTML and XML documents. This article introduces the basic usage of lxml selectors and commonly used selectors. It is hoped that readers can further master and apply lxml selectors through learning and practice, and improve the efficiency and accuracy of data extraction.

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