python简易爬虫

这篇文章主要讲解 python如何实现简易爬虫

爬虫流程

打开种子url —-> 获取种子url页面中所有的url —-> 判断是否被爬取过，未爬取过的url添加到url列表中 —-> 解析页面中需要的信息 —-> 写入数据库

上述流程中可以抽象出5个对象：

• bootstrap 启动器
• downloader 下载器
• parser 解析器
• url_manager url管理器
• outputer 输出器

启动器(main.py)

先看启动器是如何实现的：

#!/usr/bin/env python# _*_ coding:utf-8 _*_"""Created on 2017/9/23@author: tt"""import spider_outputerimport spider_parserimport spider_downloaderimport spider_url_managerclass Main:    def __init__(self):        self.urls = spider_url_manager.UrlManager()        self.downloader = spider_downloader.Downloader()        self.outputer = spider_outputer.Outputer()        self.parser = spider_parser.Parser()    def craw(self, root_url):        self.urls.add_new_url(root_url)        count = 1        while self.urls.has_new_url():            try:                new_url = self.urls.get_new_url()                print('craw %d : %s' % (count, new_url))                html_content = self.downloader.download(new_url)                new_urls, new_data = self.parser.parser(new_url, html_content)                self.urls.add_new_urls(new_urls)                self.outputer.collect_data(new_data)                count += 1            except Exception as e:                print(e)if __name__ == "__main__":    url = 'https://www.zhihu.com/people/li-xiao-miao-70/activities'    main = Main()    main.craw(url)

下载器(spider_downloader.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""import stringfrom urllib import requestfrom urllib.parse import quoteuser_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36'class Downloader:    def download(self, url):        if url is None:            return None        _url = quote(url, safe=string.printable)        req = request.Request(_url, headers={'User-Agent': user_agent})        response = request.urlopen(req)        if response.getcode() != 200:            print("request bad")            return None        html = response.read()        return html.decode('utf8')

解析器(spider_parser.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""from urllib import parsefrom bs4 import BeautifulSoupimport user_infoclass Parser:    def parser(self, page_url, html_content):        if page_url is None or html_content is None:            return        soup = BeautifulSoup(html_content, "html.parser")        new_urls = self._get_new_urls(page_url, soup)        new_data = self._get_new_data(page_url, soup)        return new_urls, new_data    def _get_new_urls(self, page_url, soup):        new_urls = set()        links = soup.find_all('a')        for link in links:            new_url = link.get('href')            new_full_url = parse.urljoin(page_url, new_url)            new_urls.add(new_full_url)        return new_urls    def _get_new_data(self, page_url, soup):        ret_data = []        author_infos = soup.find_all(class_='AuthorInfo')        print(len(author_infos))        for author_info in author_infos:            user_id = author_info.find(class_='UserLink-link').get('href')            user_id = user_id[user_id.find('e/') + 2:]            photo = author_info.find(class_='AuthorInfo-avatar').get('srcset')            pos = photo.find(' ')            photo = photo[:pos]            name = author_info.find('meta', attrs={"itemprop": "name"}).get('content')            profession = author_info.find(class_='AuthorInfo-badgeText').get_text()            user = user_info.UserInfo(user_id, name, photo, profession)            ret_data.append(user)        return ret_data

url管理器(spider_url_manager.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""class UrlManager:    def __init__(self):        self.visited_url = set()        self.visit_url = set()    def add_new_url(self, url):        if url is None:            return        if url not in self.visit_url and url not in self.visited_url:            self.visit_url.add(url)    def has_new_url(self):        return len(self.visit_url) != 0    def add_new_urls(self, urls):        if urls is None or len(urls) == 0:            return        for url in urls:            self.add_new_url(url)    def get_new_url(self):        new_url = self.visit_url.pop()        self.visited_url.add(new_url)        return new_url

输出器(spider_outputer.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""import user_daoclass Outputer:    def __init__(self):        self.user_dao = user_dao.UserDao()    def collect_data(self, data):        if data is None:            print('None')            return        else:            for d in data:                self.user_dao.add_user(d)

其他类

数据库帮助类(db_helper.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""import pymysqlclass DbHelper:    def _get_connection(self):        return pymysql.Connect(host='127.0.0.1', user='root', passwd='root', db='crawler', port=3306, charset='utf8')    def execute_update(self, sql, params):        connectin = self._get_connection()        cursor = connectin.cursor()        try:            if params is None:                s = sql            else:                s = (sql % params)            result = cursor.execute(s)            connectin.commit()            print('rows:', result)        except Exception as e:            print(e)            connectin.rollback()        finally:            cursor.close()            connectin.close()    def query(self, sql, params=None):        connection = self._get_connection()        cursor = connection.cursor()        try:            if params is None:                s = sql            else:                s = (sql % params)            cursor.execute(s)            rows = cursor.fetchall()            for row in rows:                print(row)        except Exception as e:            print(e)            connection.rollback()        finally:            cursor.close()            connection.close()

用户数据访问类(user_dao.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""import db_helperclass UserDao:    def __init__(self):        self.db = db_helper.DbHelper()    def add_user(self, user):        sql = '''INSERT IGNORE INTO zhihu_user(user_id, photo, name, profession) values('%s', '%s', '%s', '%s')'''        params = (user.user_id, user.photo, user.name, user.profession)        self.db.execute_update(sql=sql, params=params)

用户信息类(user_info.py)

#!/usr/bin/env python# -*- coding: utf-8 -*-"""Created on 2017/9/23@author: tt"""class UserInfo:    def __init__(self, user_id, name, photo, profession):        self.user_id = user_id        self.name = name        self.photo = photo        self.profession = profession    def __str__(self):        return 'UserInfo(name=' + self.name + ', photo=' + self.photo + ", profession=" + self.profession + ')\n'    def __repr__(self):        return self.__str__()

在python中print在输出对象是调用的是对象的__str__函数

这个小的demo爬取的是知乎用户id，头像，名称，职业信息