Python Web Crawling Tutorial: From Basics to a Full‑Scale Novel Scraper

Web crawlers, also known as web spiders, retrieve page content by requesting URLs such as https://www.baidu.com/ . Before writing a crawler, you should be familiar with the browser's element inspection tools (right‑click → Inspect) to locate the HTML structure you need to parse.

The first practical step is to fetch a page’s HTML. In Python 3 you can use the built‑in urllib.request module or the third‑party requests library. Install requests with:

<code>pip install requests</code>

Example using requests.get() to obtain the HTML of http://gitbook.cn/ :

<code># -*- coding:UTF-8 -*-
import requests
if __name__ == '__main__':
    target = 'http://gitbook.cn/'
    req = requests.get(url=target)
    print(req.text)
</code>

After retrieving the raw HTML, you typically need to extract the main content while discarding tags like <div> , <br> , etc. This is where BeautifulSoup shines.

Install BeautifulSoup (or beautifulsoup4 ) with either:

pip install beautifulsoup4

easy_install beautifulsoup4

Use it to parse the HTML and locate the div whose class attribute is showtxt , which contains the article body:

<code># -*- coding:UTF-8 -*-
from bs4 import BeautifulSoup
import requests
if __name__ == '__main__':
    target = 'http://www.biqukan.com/1_1094/5403177.html'
    req = requests.get(url=target)
    html = req.text
    bf = BeautifulSoup(html)
    texts = bf.find_all('div', class_='showtxt')
    print(texts[0].text.replace('\xa0'*8, '\n\n'))
</code>

For a full‑scale novel scraper, first obtain the list of chapter links. The chapter list resides in a div with class="listmain" . Each chapter link is an <a> tag with an href attribute like /1_1094/5403177.html . Combine this with the base URL to form the complete chapter URL.

Below is a compact downloader class that gathers all chapter URLs, fetches each chapter’s content, and writes it to 《一年永恒》.txt :

<code># -*- coding:UTF-8 -*-
from bs4 import BeautifulSoup
import requests, sys

class downloader(object):
    def __init__(self):
        self.server = 'http://www.biqukan.com/'
        self.target = 'http://www.biqukan.com/1_1094/'
        self.names = []  # chapter titles
        self.urls = []   # chapter URLs
        self.nums = 0

    def get_download_url(self):
        req = requests.get(url=self.target)
        html = req.text
        div_bf = BeautifulSoup(html)
        div = div_bf.find_all('div', class_='listmain')
        a_bf = BeautifulSoup(str(div[0]))
        a = a_bf.find_all('a')
        self.nums = len(a[15:])  # skip ads and extra entries
        for each in a[15:]:
            self.names.append(each.string)
            self.urls.append(self.server + each.get('href'))

    def get_contents(self, target):
        req = requests.get(url=target)
        html = req.text
        bf = BeautifulSoup(html)
        texts = bf.find_all('div', class_='showtxt')
        texts = texts[0].text.replace('\xa0'*8, '\n\n')
        return texts

    def writer(self, name, path, text):
        with open(path, 'a', encoding='utf-8') as f:
            f.write(name + '\n')
            f.writelines(text)
            f.write('\n\n')

if __name__ == "__main__":
    dl = downloader()
    dl.get_download_url()
    print('《一年永恒》开始下载：')
    for i in range(dl.nums):
        dl.writer(dl.names[i], '一念永恒.txt', dl.get_contents(dl.urls[i]))
        sys.stdout.write("  已下载:%.3f%%" % (float(i)/dl.nums*100) + '\r')
        sys.stdout.flush()
    print('《一年永恒》下载完成')
</code>

The script runs in a single process, sequentially downloading each chapter and displaying progress. After completion, you will have a plain‑text file containing the entire novel.

Overall, this guide walks you through inspecting HTML, using requests to fetch pages, parsing with BeautifulSoup , extracting links and content, and assembling a functional web crawler in Python.