python爬虫入门（一）

使用requests 库获取网站html信息

import requests
response = requests.get("https://jingyan.baidu.com/article/17bd8e52c76b2bc5ab2bb8a2.html#:~:text=1.%E6%89%93%E5%BC%80%E6%B5%8F%E8%A7%88%E5%99%A8F12%202.%E6%89%BE%E5%88%B0headers%E9%87%8C%E9%9D%A2%E7%9A%84cookie,3.%E5%A6%82%E6%9E%9C%E8%A6%81%E6%89%BE%E5%88%B0%E5%AF%B9%E5%BA%94%E7%9A%84%E7%82%B9%E5%87%BBcookie%204.%E8%BF%9E%E7%BB%AD%E4%B8%89%E6%AC%A1%E7%82%B9%E5%87%BB%E5%8F%B3%E9%94%AE%E5%A4%8D%E5%88%B6")
print(response) # <Response [200]>  返回 Response类型实例
print(response.status_code)  # 200 返回状态码

# 用状态码判断是否获取成功
if response.status_code >= 200 and response.status_code < 400:
  ... #  获取响应主体内容
elif response.status_code >= 400 and response.status_code < 500:
  print("request failed for the client has error客户端错误")
elif response.status_code >= 500:
  print("request failed for the server has error服务端错误")


if response.ok:
  print(response.text) # 返回网页源码
  ...  # 获取响应主体内容
else:
  print("request failed")


# 直接使用以下代码，出现“418”错误；因为该网站想过滤掉爬虫程序，只想服务正常用户；
import requests
response = requests.get("https://movie.douban.com/top250")
print(response) # <Response [200]>  返回 Response类型实例
print(response.text)  # 返回网页源码

# 伪装,增加headers，具体可以从F12开发者工具的 -> network -> user-agent里面寻找
import requests
headers = {
    "User-Agent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36"
}
response = requests.get("https://movie.douban.com/top250", headers=headers)
print(response) # <Response [200]>  返回 Response类型实例
print(response.text)  # 返回网页源码

HTML简单结构入门

HTML  定义网页的结构和信息，文件名为xxx.html,用浏览器打开
CSS  定义网页样式
JavaScript 定义用户和网页的交互逻辑

<!DOCTYPE HTML>
<html>
  <body>
    <h1>title</h1>
    <p>some texts</p>
  </body>
</html>

标题
<h1></h1>
<h2></h2>
<h3></h3>
<h4></h4>
<h5></h5>
<h6></h6>

文本段落
<p></p>
强制换行 <br>
加粗 <b></b>
斜体 <i></i>
下划线 <u></u>
图片 <img src="..." width="" height="">
链接 <a href="https://..." target="_self">text</a> (target表示打开的方式，当前页面跳转，新页面跳转等)
容器 块级元素-div-独占一行，span为内嵌元素
<div>
  ...
</div>

<span>
  ...
</span>

列表 有序列表ol，无序列表ul
<ol>
    <li>chinese</li>
    <li>math</li>
</ol>

<ul>
    <li>chinese</li>
    <li>math</li>
</ul>

表格 td数据，
<table border=“1”> 表格属性之一，显示边框
<table>
    <table border=“1”>
    <thead>
        <tr>
            <td>tableheader1</td>
            <td>tableheader2</td>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>111</td>
            <td>2222</td>
        </tr>
        <tr>
            <td>333</td>
            <td>444</td>
        </tr>
    </tbody>
</table>

class属性 -- 帮助分类
<p class="content">给岁月以文明</p>
<p class="content">而不是给文明以岁月</p>
<p class="review">五星好评！</p>

在这里插入图片描述

爬取网页中的书的价格和名称

# 解析,找网页中商品的price和书名
from bs4 import BeautifulSoup
import requests
content = requests.get("http://books.toscrape.com/").text()
soup = BeautifulSoup(content, "html.parser")  # 返回树状解析结构

all_prices = soup.findAll("p", attrs={"class":"price_color"})
for price in all_prices:  
  print(prices.string[2:])

all_titles = soup.findAll("h3")
for title in all_titles:
  all_links = title.findAll("a")  # 寻找所有a
  # all_links = title.find("a")   # 寻找第一个a
  for link in all_links:
    print(link.string)