Python 爬虫入门 Day 3 - 实现爬虫多页抓取与翻页逻辑

Python 第二阶段 - 爬虫入门

🎯 今日目标

• 掌握网页分页的原理和定位“下一页”的链接
• 能编写循环逻辑自动翻页抓取内容
• 将多页抓取整合到爬虫系统中

📘 学习内容详解

1. 🔁 网页分页逻辑介绍
   以 quotes.toscrape.com 为例：

• 首页链接：https://quotes.toscrape.com/
• 下一页链接：<li class="next"><a href="/page/2/">Next</a></li>

我们可以通过 BeautifulSoup 查找li.next > a['href'] 获取下一页地址，并拼接 URL。

2. 🧪 核心思路伪代码

   while True:
       1. 请求当前页 URL
       2. 解析 HTML，提取所需内容
       3. 判断是否存在下一页链接
           - 如果有，拼接新 URL，继续循环
           - 如果没有，break 退出循环
   

💻 示例代码（多页抓取）

import requests
from bs4 import BeautifulSoup
from urllib.parse import urljoin

def scrape_all_quotes(start_url):
    quotes = []
    url = start_url

    while url:
        print(f"正在抓取：{url}")
        res = requests.get(url)
        soup = BeautifulSoup(res.text, 'lxml')

        for quote_block in soup.find_all("div", class_="quote"):
            quote_text = quote_block.find("span", class_="text").text.strip()
            author = quote_block.find("small", class_="author").text.strip()
            tags = [tag.text for tag in quote_block.find_all("a", class_="tag")]

            quotes.append({
                "quote": quote_text,
                "author": author,
                "tags": tags
            })

        # 查找下一页
        next_link = soup.select_one("li.next > a")
        if next_link:
            next_href = next_link['href']
            url = urljoin(url, next_href)  # 拼接为完整URL
        else:
            url = None

    return quotes

if __name__ == "__main__":
    all_quotes = scrape_all_quotes("https://quotes.toscrape.com/")
    print(f"共抓取到 {len(all_quotes)} 条名言")

    # 示例输出前3条
    for quote in all_quotes[:3]:
        print(f"\n{quote['quote']}\n—— {quote['author']}｜标签：{', '.join(quote['tags'])}")

🧠 今日练习任务

• 修改已有爬虫，实现抓取所有页面的名言数据

• 使用 len() 查看共抓取多少条数据

• 额外挑战：将所有数据保存为 JSON 文件（使用 json.dump）

  练习代码：

  import requests
  from bs4 import BeautifulSoup
  from urllib.parse import urljoin
  import json
  
  def scrape_all_quotes(start_url):
      quotes = []
      url = start_url
  
      while url:
          print(f"抓取页面：{url}")
          response = requests.get(url)
          soup = BeautifulSoup(response.text, "lxml")
  
          quote_blocks = soup.find_all("div", class_="quote")
          for block in quote_blocks:
              text = block.find("span", class_="text").text.strip()
              author = block.find("small", class_="author").text.strip()
              tags = [tag.text for tag in block.find_all("a", class_="tag")]
  
              quotes.append({
                  "quote": text,
                  "author": author,
                  "tags": tags
              })
  
          # 找到下一页链接
          next_link = soup.select_one("li.next > a")
          if next_link:
              next_href = next_link['href']
              url = urljoin(url, next_href)
          else:
              url = None
  
      return quotes
  
  if __name__ == "__main__":
      start_url = "https://quotes.toscrape.com/"
      all_quotes = scrape_all_quotes(start_url)
  
      print(f"\n共抓取到 {len(all_quotes)} 条名言。\n")
  
      # 保存到 JSON 文件
      output_file = "quotes.json"
      with open(output_file, "w", encoding="utf-8") as f:
          json.dump(all_quotes, f, ensure_ascii=False, indent=2)
  
      print(f"数据已保存到文件：{output_file}")
  

  运行输出：

  正在抓取：https://quotes.toscrape.com/
  正在抓取：https://quotes.toscrape.com/page/2/
  正在抓取：https://quotes.toscrape.com/page/3/
  正在抓取：https://quotes.toscrape.com/page/4/
  正在抓取：https://quotes.toscrape.com/page/5/
  正在抓取：https://quotes.toscrape.com/page/6/
  正在抓取：https://quotes.toscrape.com/page/7/
  正在抓取：https://quotes.toscrape.com/page/8/
  正在抓取：https://quotes.toscrape.com/page/9/
  正在抓取：https://quotes.toscrape.com/page/10/
  共抓取到 100 条名言
  数据已保存到文件：quotes.json
  

  quotes.json文件输出：

  [
    {
      "quote": "“The world as we have created it is a process of our thinking. It cannot be changed without changing our thinking.”",
      "author": "Albert Einstein",
      "tags": [
        "change",
        "deep-thoughts",
        "thinking",
        "world"
      ]
    },
    {
      "quote": "“It is our choices, Harry, that show what we truly are, far more than our abilities.”",
      "author": "J.K. Rowling",
      "tags": [
        "abilities",
        "choices"
      ]
    },
    {
      "quote": "“There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.”",
      "author": "Albert Einstein",
      "tags": [
        "inspirational",
        "life",
        "live",
        "miracle",
        "miracles"
      ]
    },
    ... # 此处省去95条数据
    {
      "quote": "“A person's a person, no matter how small.”",
      "author": "Dr. Seuss",
      "tags": [
        "inspirational"
      ]
    },
    {
      "quote": "“... a mind needs books as a sword needs a whetstone, if it is to keep its edge.”",
      "author": "George R.R. Martin",
      "tags": [
        "books",
        "mind"
      ]
    }
  

📎 小技巧

• urljoin(base_url, relative_path) 可以自动拼接绝对路径

• 网站有时采用 JavaScript 动态分页 —— 这类网站需用 Selenium/Playwright（后续学习）

📝 今日总结

• 学会了如何从网页中提取“下一页”链接
• 掌握了自动翻页抓取逻辑的实现方式
• 距离构建完整的数据采集工具更进一步