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爬虫

爬虫原理

• 爬虫，又称网络爬虫，是一种自动获取网页内容的程序。
• 它模拟人类浏览网页的行为，发送HTTP请求，获取网页源代码，再通过解析、提取等技术手段，获取所需数据。

HTTP请求与响应过程

• 爬虫首先向目标网站发送HTTP请求，请求可以包含多种参数，如URL、请求方法（GET或POST）、请求头（Headers）等。
• 服务器接收到请求后，返回相应的HTTP响应，包括状态码、响应头和响应体（网页内容）。

常用爬虫技术

实战

1. 爬取豆瓣电影Top250

import requests
from bs4 import BeautifulSoup
import csv
# 请求 URL
url = 'https://movie.douban.com/top250'
# 请求头部
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36'
}
# 解析页面函数
def parse_html(html):soup = BeautifulSoup(html, 'lxml')movie_list = soup.find('ol', class_='grid_view').find_all('li')for movie in movie_list:title = movie.find('div', class_='hd').find('span', class_='title').get_text()rating_num = movie.find('div', class_='star').find('span', class_='rating_num').get_text()comment_num = movie.find('div', class_='star').find_all('span')[-1].get_text()writer.writerow([title, rating_num, comment_num])# 保存数据函数
def save_data():f = open('douban_movie_top250.csv', 'a', newline='', encoding='utf-8-sig')global writerwriter = csv.writer(f)writer.writerow(['电影名称', '评分', '评价人数'])for i in range(10):url = 'https://movie.douban.com/top250?start=' + str(i*25) + '&filter='response = requests.get(url, headers=headers)parse_html(response.text)f.close()if __name__ == '__main__':save_data()

2. 爬取当当网图书信息

import requests
from lxml import etree
import csvurl = 'http://search.dangdang.com/?key=Python&act=input'
headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36'
}def parse_html(html):selector = etree.HTML(html)book_list = selector.xpath('//*[@id="search_nature_rg"]/ul/li')for book in book_list:title = book.xpath('a/@title')if title:title = title[0]else:title = "未知书名"link = book.xpath('a/@href')if link:link = link[0]else:link = "未知链接"price = book.xpath('p[@class="price"]/span[@class="search_now_price"]/text()')if price:price = price[0]else:price = "未知价格"author = book.xpath('p[@class="search_book_author"]/span[1]/a/@title')if author:author = author[0]else:author = "未知作者"publish_date = book.xpath('p[@class="search_book_author"]/span[2]/text()')if publish_date:publish_date = publish_date[0]else:publish_date = "未知出版日期"publisher = book.xpath('p[@class="search_book_author"]/span[3]/a/@title')if publisher:publisher = publisher[0]else:publisher = "未知出版社"yield {'书名': title,'链接': link,'价格': price,'作者': author,'出版日期': publish_date,'出版社': publisher}def save_data():response = requests.get(url, headers=headers)if response.status_code == 200:with open('dangdang_books.csv', 'w', newline='', encoding='utf-8-sig') as f:writer = csv.writer(f)writer.writerow(['书名', '链接', '价格', '作者', '出版日期', '出版社'])for item in parse_html(response.text):writer.writerow([item['书名'], item['链接'], item['价格'], item['作者'], item['出版日期'], item['出版社']])else:print(f"请求失败，状态码：{response.status_code}")if __name__ == '__main__':save_data()