python爬虫的一些代码

你好，欢迎查看我的第5个笔记。这是本人为了保存一些代码而写的博客，由于精力实在有限，无法从头开始介绍爬虫相关的知识故仅仅罗列了几段代码案例

1.编写url管理器

class UrlManager():
    """
    url管理器罢了
    """
    def __init__(self):
        self.new_urls=set()
        self.old_urls=set()

    def add_new_url(self,url):
        if url is None or len(url)==0:
            return
        if url in self.new_urls or url in self.old_urls:
            return
        self.new_urls.add(url)

    def add_new_urls(self,urls):
        if urls is None or len(urls)==0:
            return
        for url in urls:
            self.new_urls.add(url)

    def get_url(self):
        if self.is_has_url():
            url = self.new_urls.pop()
            self.old_urls.add(url)
            return url
        else:
            return None

    def is_has_url(self):
        return len(self.new_urls) > 0

要先创建一个包（utils），在里面建个py文件(url_manager),里面写上面的代码

像这样：

2.爬取www.crazyant.net的全部标题网页

import requests
from bs4 import BeautifulSoup
from utils import url_manager
import re


fout=open("crazyant_all_pages.text","w")

root_url ="http://www.crazyant.net"#定义入口网站
urls=url_manager.UrlManager()#实例化UrlManager类
urls.add_new_url(root_url)#调用add_new_url()方法，把入口网站放在new_urls里面

while urls.is_has_url():#当new_urls里面有网站时
    cur_url=urls.get_url()#从newurls里面拿出一个网站
    r=requests.get(cur_url,timeout=3)#发送request，抓取r的信息
    soup=BeautifulSoup(r.text,"html.parser")#用html。parser解析r
    title=soup.title.string#抓取r的title信息
    print("success: %s,%s\n" % (cur_url, title))#打印cur_url 和 title
    fout.write("%s\t%s\n"%(cur_url,title))
    links=soup.find_all("a")#得到所有的a标签
    pattern=r'^http://www.crazyant.net/\d+.html$'#设置正则语句
    for link in links:##遍历每一个a
        href=link["href"]#得到每个a的链接
        if href is None or len(href)==0:
            continue
        if re.match(pattern,href) :
            urls.add_new_url(href)
fout.close()

注：www.crazyant.net是b站up主的个人博客，见下面链接[3.2]--Python爬虫实战爬取所有博客页面_哔哩哔哩_bilibili

附一张up主的主页图片

3.爬取四川农业大学教务网的通知

import requests
from bs4 import BeautifulSoup
fout = open("jiaowu_Notice.text","w",encoding="utf8")
url ="https://jiaowu.sicau.edu.cn/web/web/web/gwmore.asp"
response=requests.get(url)
response.encoding="gb2312"
soup = BeautifulSoup(response.text,"html.parser")
form=soup.find("form",attrs={"method":"post"})
trs=form.find_all("tr",attrs={"class":"text-c"})
num=1
for tr in trs:
    links=tr.find("div",attrs={"align":"left"})
    if links is None or len(links) == 0:
        continue
    for link in links:
        try:
            href=link["href"]
            if href is None or len(href) == 0:
                continue
            print(f"{num}.  https://jiaowu.sicau.edu.cn/web/web/web/{href}\t{link.get_text()}\n")
            num+=1
            fout.write(f"{num}.\thttps://jiaowu.sicau.edu.cn/web/web/web/{href}\t{link.get_text()}\n")
        except:
            pass
fout.close()

4.爬取打印四川农业大学理学院所有的通知告示

import requests
from bs4 import BeautifulSoup
num=0
url_list=["https://lixueyuan.sicau.edu.cn/xwjtz/tzgg.htm"]
for n in [2,3]:
    url_list.append(f"https://lixueyuan.sicau.edu.cn/xwjtz/tzgg/{n}.htm")
for url in url_list:
    r=requests.get(url)
    r.encoding="utf8"
    soup=BeautifulSoup(r.text,"html.parser")
    lis=soup.find("div",attrs={"class":"newm"}).find_all("li")

    for li in lis:
        a=li.find("a")
        text_list=a.get_text().split("\n")
        text = text_list[1]
        time = text_list[2]
        href=a["href"].strip("..")
        num+=1
        print(f"{num}\thttps://lixueyuan.sicau.edu.cn{href}\t{time}\t{text}")