【Foundation】Web Crawler Practical: Scraping Static Web Page Text Data

# 2.1 HTTP Protocol and Web Page Structure Analysis

## 2.1.1 Fundamental Principles of HTTP Protocol

HTTP (Hypertext Transfer Protocol) is an application layer protocol used to transmit data between web browsers and web servers. Based on a request-response model, the client (typically a web browser) sends an HTTP request to the server, which processes the request and returns an HTTP response.

An HTTP request consists of the following parts:

* Request Line: Specifies the request method (e.g., GET, POST), the requested resource path, and the HTTP version.
* Request Headers: Contains additional information about the client and the request, such as User-Agent, Accept, and Content-Type.
* Request Body: Contains the data of the request (optional).

An HTTP response consists of the following parts:

* Status Line: Contains the HTTP status code (e.g., 200 OK), status message, and HTTP version.
* Response Headers: Contains additional information about the response, such as Content-Type, Content-Length, and Date.
* Response Body: Contains the data of the response (optional).

# 2. Web Page Text Data Crawling Practice

## 2.1 HTTP Protocol and Web Page Structure Analysis

### 2.1.1 Fundamental Principles of HTTP Protocol

HTTP (Hypertext Transfer Protocol) is a protocol for transmitting data between Web clients and servers. It is a stateless protocol, which means that each request is independent and the server does not store any information about the client's state.

An HTTP request consists of the following parts:

***Request Line:** Specifies the request method (e.g., GET or POST), the requested resource (e.g., URL), and the HTTP version.
***Request Headers:** Contains additional information about the client and the request, such as User-Agent, Content-Type, and Cookie.
***Request Body:** If the request is a POST request, it contains the data to be submitted to the server.

An HTTP response consists of the following parts:

***Status Line:** Specifies the response status code (e.g., 200 OK or 404 Not Found) and the HTTP version.
***Response Headers:** Contains additional information about the response, such as Content-Type, Content-Length, and Cache-Control.
***Response Body:** Contains the data sent from the server to the client.

### 2.1.2 Composition and Analysis of Web Page Structure

A web page is written in HTML (Hypertext Markup Language), which defines the structure and content of the web page. An HTML document consists of the following elements:

***Tags:** Used to define web page elements, such as titles, paragraphs, and lists.
***Attributes:** Provide additional information for tags, such as ID, class, and style.
***Content:***

***arse a web page, understanding HTML syntax and using parsing libraries such as Beautiful Soup or lxml is necessary. These libraries can convert an HTML document into an object tree, allowing easy access and manipulation of web page elements.

## 2.2 Web Page Text Data Extraction Techniques

### 2.2.1 Regular Expression Matching

Regular expressions are a powerful tool for matching string patterns. They can be used to extract specific text data from web pages, such as email addresses, phone numbers, and dates.

Regular expression syntax includes:

***Character Classes:** Match specific character sets, such as letters, numbers, and punctuation