Python 爬虫基础

1.1 理论

在浏览器通过网页拼接【/robots.txt】来了解可爬取的网页路径范围

例如访问： https://www.csdn.net/robots.txt

User-agent: *
Disallow: /scripts
Disallow: /public
Disallow: /css/
Disallow: /images/
Disallow: /content/
Disallow: /ui/
Disallow: /js/
Disallow: /scripts/
Disallow: /article_preview.html*
Disallow: /tag/
Disallow: /?
Disallow: /link/
Disallow: /tags/
Disallow: /news/
Disallow: /xuexi/

通过Python Requests 库发送HTTP【Hypertext Transfer Protocol “超文本传输协议”】请求

通过Python Beautiful Soup 库来解析获取到的HTML内容

HTTP请求

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HTTP响应

在这里插入图片描述

1.2 实践代码【获取价格&书名】

import requests
# 解析HTML
from bs4 import BeautifulSoup# 将程序伪装成浏览器请求
head = {"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)"
}
requests = requests.get("http://books.toscrape.com/",headers= head)
# 指定编码
# requests.encoding= 'gbk'
if requests.ok:# file = open(r'C:\Users\root\Desktop\Bug.html', 'w')# file.write(requests.text)# file.closecontent =  requests.text## html.parser 指定当前解析 HTML 元素soup = BeautifulSoup(content, "html.parser")## 获取价格all_prices = soup.findAll("p", attrs={"class":"price_color"})for price in all_prices:print(price.string[2:])## 获取名称all_title = soup.findAll("h3")for title in all_title:## 获取h3下面的第一个a元素print(title.find("a").string)
else:print(requests.status_code)

1.3 实践代码【获取 Top250 的电影名】

import requests
# 解析HTML
from bs4 import BeautifulSoup
head = {"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)"
}
# 获取 TOP 250个电影名
for i in range(0,250,25):response = requests.get(f"https://movie.douban.com/top250?start={i}", headers= head)if response.ok:content =  response.textsoup = BeautifulSoup(content, "html.parser")all_titles = soup.findAll("span", attrs={"class": "title"})for title in all_titles:if "/" not in title.string:print(title.string) else:print(response.status_code)

1.4 实践代码【下载图片】

import requests
# 解析HTML
from bs4 import BeautifulSouphead = {"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)"
}
response = requests.get(f"https://www.maoyan.com/", headers= head)
if response.ok:soup = BeautifulSoup(response.text, "html.parser")for img in soup.findAll("img", attrs={"class": "movie-poster-img"}):img_url = img.get('data-src')alt = img.get('alt')path = 'img/' + alt + '.jpg'res = requests.get(img_url)with open(path, 'wb') as f:f.write(res.content)
else:print(response.status_code)