Use Python to teach you step by step how to implement a crawler (including front-end interface)

Preface
Basic principles of crawlers
Send HTTP requests using Python’s requests library
Use the BeautifulSoup library to parse HTML pages
Build front-end interface using PyQt5
Implement a complete crawler program
Conclusion

Preface

With the rapid development of the Internet and the earth-shaking technological innovations in the technology circle, massive amounts of data are generated on the Internet every day, which is of great value to both businesses and individuals. As a developer, you are no stranger to data processing, and you should also be familiar with using python, because the python language has become popular in junior high school. You must also be familiar with crawlers, one of the main functions of python. In fact, crawlers (also A web spider (called a web spider) is a tool that can automatically crawl web data. It can help us obtain the information we need from the web. So the topic of this issue is about the simple use of crawlers. This article will teach you step by step how to use Python to implement a simple crawler, and use PyQt5 to build a simple front-end interface to display the crawled data. This article will start with the basic principles of crawlers, then introduce how to use Python's requests library to send HTTP requests, and how to use the BeautifulSoup library to parse HTML pages, and finally implement a complete crawler program. I hope to be able to understand the development of this article. Fellow readers are helpful and inspiring.

Basic principles of crawlers

As a programmer, you must be familiar with the concept of a crawler. Let’s take a look at the basic principles of a crawler. The working principle of a crawler is actually very simple. It first sends an HTTP request to the target website, and then parses the HTML page returned by the server to extract all the information. The required information can be text, pictures, links, etc. At the same time, the crawler can use this information to determine whether it needs to continue crawling the page and how to crawl other links to the page. In addition, the crawler is mainly implemented through the python language. This article also uses the python language as an example language for introduction. Let’s share the design ideas of the crawler, as shown in the figure below:

Send HTTP requests using Python’s requests library

Friends who have used Python must know that its third-party library is very powerful and easy to use. Here I would like to introduce Python’s library about network requests: requests. In other words, Python’s requests library is a very popular HTTP library. It can Help us developers send HTTP requests easily.

The specific steps to use the requests library to send HTTP requests are divided into the following steps:

Import requests library;
Create a Session object;
Use Session object to send HTTP request;
Get the response of an HTTP request.

Next, I will share the specific usage method. Here is a sample code that uses the requests library to send HTTP requests:

import requests 

# 创建一个Session对象 
session = requests.Session() 

# 发送HTTP请求 
response = session.get('https://www.baidu.com') 

# 获取HTTP请求的响应
print(response.text)

Use the BeautifulSoup library to parse HTML pages

Next, let’s introduce the third-party library for parsing HTML pages. There are also corresponding libraries in python to support parsing HTML pages. BeautifulSoup is a very popular HTML parsing library, which can help us parse HTML pages easily. The specific steps to use the BeautifulSoup library to parse HTML pages are as follows:

Import the BeautifulSoup library
Create a BeautifulSoup object
Parse HTML pages using BeautifulSoup objects
Get parsing results

Next, I will share the specific usage method. Here is a sample code that uses the BeautifulSoup library to parse HTML pages:

from bs4 import BeautifulSoup

# 创建一个BeautifulSoup对象
soup = BeautifulSoup(html_doc, 'html.parser')

# 获取解析结果
print(soup.title.text)

Build front-end interface using PyQt5

Next, I will share the last part of this article's topic, which is to display the data crawled by the crawler through the front-end interface. Here, PyQt5 is used to build the front-end interface. In fact, PyQt5 is a cross-platform GUI library, which can help us easily build a graphical interface. The specific steps to use PyQt5 to build the front-end interface are as follows:

Import PyQt5 library
Create a QApplication object
Create a main window object
Add controls to the main window object
Set the properties of the control
Signals and slots for connecting controls

Next, share the specific usage method. Here is a sample code for using PyQt5 to build a front-end interface:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QLabel

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        # 设置窗口标题
        self.setWindowTitle("爬虫")

        # 创建一个按钮
        self.button = QPushButton("开始爬虫")

        # 创建一个标签
        self.label = QLabel("爬虫结果")

        # 设置按钮的槽函数
        self.button.clicked.connect(self.on_button_clicked)

        # 在主窗口对象中添加控件
        self.setCentralWidget(self.button)

        # 设置控件的属性
        self.label.setAlignment(Qt.AlignCenter)

        # 显示窗口
        self.show()

    def on_button_clicked(self):
        # 爬虫逻辑

        # 更新标签的内容
        self.label.setText("爬虫完成")

# 创建一个QApplication对象
app = QApplication(sys.argv)

# 创建一个主窗口对象
window = MainWindow()

# 进入主循环
sys.exit(app.exec_())

Implement a complete crawler program

After using the two key third-party libraries shared above, we will combine the previous two knowledge points to implement a complete crawler program. This crawler will start from the specified URL, crawl all links on the page, and then store these links in a file. The specific sample code is as follows:

import requests
from bs4 import BeautifulSoup
import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QLabel

# 要抓取的URL
url = 'https://www.baidu.com'

# 创建一个Session对象
session = requests.Session()

# 发送HTTP请求
response = session.get(url)

# 获取HTTP请求的响应
html_doc = response.text

# 创建一个BeautifulSoup对象
soup = BeautifulSoup(html_doc, 'html.parser')

# 获取所有链接
links = soup.find_all('a')

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        # 设置窗口标题
        self.setWindowTitle("爬虫")

        # 创建一个按钮
        self.button = QPushButton("开始爬虫")

        # 创建一个标签
        self.label = QLabel("爬虫结果")

        # 设置按钮的槽函数
        self.button.clicked.connect(self.on_button_clicked)

        # 在主窗口对象中添加控件
        self.setCentralWidget(self.button)

        # 设置控件的属性
        self.label.setAlignment(Qt.AlignCenter)

        # 显示窗口
        self.show()

    def on_button_clicked(self):
        # 爬虫逻辑

        # 更新标签的内容
        self.label.setText("爬虫完成")

# 创建一个QApplication对象
app = QApplication(sys.argv)

# 创建一个主窗口对象
window = MainWindow()

# 进入主循环
sys.exit(app.exec_())

Conclusion

Through this article's introduction to using Python to implement the crawler function, and using Python to implement a simple crawler example, readers must have learned it, right? This article starts with the basic principles of crawlers, then introduces how to use Python's requests library to send HTTP requests, and how to use the BeautifulSoup library to parse HTML pages, and finally displays the crawled data on the front-end interface. Finally, These disassembled knowledge points are combined to implement a complete crawler program. Since this case is a simple crawler program, what this article introduces is only a relatively simple example. I hope it can bring some inspiration to readers. If readers want to have a deeper understanding and use of crawlers, please go to the python developer community to find ideas. I also hope that Big guys in python-related fields will let it go, experts please let it go. I hope this tutorial can help you learn crawlers and implement your own crawler program, thank you for watching! Welcome to communicate in the comment area!