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Several ways to extract data from HTML pages

王林

Jun 13, 2023 am 10:40 AM

crawler technologyData Extractionhtml parsing

HTML page is the most common type of Internet page. It is written in the form of markup language and includes many tags and elements. In many cases, we need to extract data from HTML pages so that the pages can be correctly analyzed, managed, and processed. This article will introduce some methods to extract data from HTML pages to help readers complete this task easily.

1. Using regular expressions

Regular expressions are a commonly used tool in text processing and one of the most basic methods for extracting data from HTML pages. It can match the required data based on specific patterns and extract the required information.

For example, if we want to extract all image links from an HTML page, we can use the following regular expression:

<img  src="/static/imghwm/default1.png"  data-src="([wW]*?)"  class="lazy" .*?.*? alt="Several ways to extract data from HTML pages" >

This regular expression will match all img tags , and extract the value of the src attribute, which is the link to the image.

It should be noted that the regular expression needs to be adjusted according to the situation. If the structure and content of the HTML page change, then the regular expression needs to be rewritten.

2. Use the parser

The parser is more flexible and efficient than regular expressions. It can parse various tags and elements in HTML pages and extract the required content.

For example, the BeautifulSoup library in Python is a very easy-to-use parser. It can easily find specific tags in HTML pages and extract the required data from them.

The following is a simple Python example code, through which all hyperlinks can be extracted from an HTML document:

from bs4 import BeautifulSoup

html = '''<html><body><div id="content"><a href="http://www.baidu.com">百度一下</a></div></body></html>'''

soup = BeautifulSoup(html, 'html.parser')
for link in soup.find_all('a'):
    print(link.get('href'))

This code will output: http://www .baidu.com.

3. Use XPath

XPath is a query language in XML documents and can also be applied in HTML pages. It can select a specific node or set of nodes in the document based on a path expression.

Many mainstream programming languages now have built-in XPath parsers. For example, the built-in standard library xml.etree.ElementTree in Python provides XPath support.

The following is a simple Python example code, through which all hyperlinks can be extracted from an HTML document:

import xml.etree.ElementTree as ET

html = '''<html><body><div id="content"><a href="http://www.baidu.com">百度一下</a></div></body></html>'''

tree = ET.fromstring(html)
for link in tree.findall('.//a'):
    print(link.get('href'))

This code will output: http://www .baidu.com.

Summary

The above introduces three methods of extracting data from HTML pages. They all have their own advantages and disadvantages. In practical applications, we need to choose the most appropriate method according to the specific situation. No matter which method is used, we need to have a certain understanding of the structure and markup language in HTML pages, so that we can more accurately extract the data we need.

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