Python3爬虫(1)_使用Urllib进行网络爬取

网络爬虫

又被称为网页蜘蛛，网络机器人，在FOAF社区中间，更经常的称为网页追逐者，是一种按照一定的规则，自动地抓取万维网信息的程序或者脚本。另外一些不常使用的名字还有蚂蚁、自动索引、模拟程序或者蠕虫。

（参考百度百科，详细请见https://baike.baidu.com/item/网络爬虫/5162711?fr=aladdin&fromid=22046949&fromtitle=%E7%88%AC%E8%99%AB）

代码和步骤说明：借鉴http://cuijiahua.com。 https://blog.csdn.net/c406495762/article/details/58716886

Urllib

urllib是一个URL处理包，这个包中集合了一些处理URL的模块，如下：

打开和读取URL：urllib.request
包含request产生的错误，可以使用try进行捕捉处理：urllib.error
包含解析URLs的方法：urllib.parse
urllib.robotparser模块用来解析robots.txt文本文件.它提供了一个单独的RobotFileParser类，通过该类提供的can_fetch()方法测试爬虫是否可以下载一个页面

urllib_test01.py

 from urllib import request

 if __name__=="__main__":

     response=request.urlopen("http://i.cnblogs.com")

     html=response.read()

     print(html)

运行结果：

>>>
RESTART: C:\Users\DELL\AppData\Local\Programs\Python\Python36\urllib_test01.py
b'\r\n<!DOCTYPE html>\r\n<html>\r\n<head>\r\n <meta charset="utf-8" />\r\n <meta name="viewport" content="width=device-width" />\r\n <title>\xe7\x94\xa8\xe6\x88\xb7\xe7\x99\xbb\xe5\xbd\x95 - \xe5\x8d\x9a\xe5\xae\xa2\xe5\x9b\xad</title>\r\n <link rel="stylesheet" href="/scripts/bootstrap/css/bootstrap.min.css" />\r\n <link href="/scripts/ladda/ladda-themeless.min.css" rel="stylesheet" />\r\n <link href="/css/signin_bundle.css?v=L6jW_dned1XSxz8ohN2oMp1Q1fPUq1W5sWqqw6HNaH01" type="text/css" rel="stylesheet" /> \r\n <script src="/scripts/jquery.min.js"></script>\r\n <script src="/scripts/bootstrap/js/bootstrap.min.js"></script>\r\n <script src="/scripts/ladda/spin.min.js"></script>\r\n <script src="/scripts/ladda/ladda.min.js"></script>\r\n <script src="/scripts/jsencrypt.min.js"></script>\r\n <script>\r\n var return_url = \'http://i.cnblogs.com/\';\r\n var ajax_url = \'/user\' + \'/signin\';\r\n var enable_captcha = false;\r\n var is_in_progress = false;\r\n </script>\r\n <script src="/scripts/signin_bundle.js?v=1spnpY8gb0K9MfNetxJoLoPjd7dN7PIKB8kMqcak-RQ1"></script>\r\n\r\n</head>\r\n<body onload="setFocus()">\r\n <div style="width: 100%;">\r\n <div align="center">\r\n <div id="Main">\r\n <noscript>\r\n <div style="font-size:15px;margin-bottom:20px;">\r\n \xe6\x82\xa8\xe7\x9a\x84\xe6\xb5\x8f\xe8\xa7\x88\xe5\x99\xa8\xe6\x9c\xaa\xe5\x90\xaf\xe7\x94\xa8Javascript\xef\xbc\x8c\xe6\x97\xa0\xe6\xb3\x95\xe8\xbf\x9b\xe8\xa1\x8c\xe7\x99\xbb\xe5\xbd\x95\xe3\x80\x82\r\n </div>\r\n <style>\r\n form {\r\n display: none;\r\n }\r\n </style>\r\n </noscript>\r\n <form method="post" onsubmit="return false;">\r\n <div id="Heading">\xe7\x99\xbb\xe5\xbd\x95\xe5\x8d\x9a\xe5\xae\xa2\xe5\x9b\xad - \xe4\xbb\xa3\xe7\xa0\x81\xe6\x94\xb9\xe5\x8f\x98\xe4\xb8\x96\xe7\x95\x8c</div>\r\n <div class="block">\r\n <label class="label-line">\xe7\x99\xbb\xe5\xbd\x95\xe7\x94\xa8\xe6\x88\xb7\xe5\x90\x8d(<a href="/GetUsername.aspx" tabindex="-1" class="tb_right">\xe6\x89\xbe\xe5\x9b\x9e</a>)</label>\r\n <input type="text" id="input1" value="" class="input-text" onkeydown="check_enter(event)" /> <span id="tip_input1" class="tip"></span>\r\n </div>\r\n <div class="block">\r\n <label class="label-line">\xe5\xaf\x86\xe7\xa0\x81(<a href="/GetMyPassword.aspx" tabindex="-1" class="tb_right">\xe9\x87\x8d\xe7\xbd\xae</a>)</label>\r\n <input type="password" id="input2" value="" class="input-text" onkeydown="check_enter(event)" /> <span id="tip_input2" class="tip"></span>\r\n </div>\r\n\r\n <div class="modal fade" id="checkWay" tabindex="-1" role="dialog" aria-hidden="true">\r\n <div class="modal-dialog">\r\n <div class="modal-content center-block">\r\n <div class="modal-header">\r\n <button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">×</span><span class="sr-only">Close</span></button>\r\n <h4 class="modal-title">\r\n \xe8\xaf\xb7\xe5\xae\x8c\xe6\x88\x90\xe4\xba\xba\xe6\x9c\xba\xe8\xaf\x86\xe5\x88\xab\xe9\xaa\x8c\xe8\xaf\x81\r\n </h4>\r\n </div>\r\n <div class="modal-body">\r\n <div id="showLoading" class="ladda-button" data-style="zoom-in"></div>\r\n <div id="captchaBox" class="center-block">\r\n <span id="geetestLoading"> \xe9\xaa\x8c\xe8\xaf\x81\xe7\xa0\x81\xe7\xbb\x84\xe4\xbb\xb6\xe5\x8a\xa0\xe8\xbd\xbd\xe4\xb8\xad,\xe8\xaf\xb7\xe7\xa8\x8d\xe5\x90\x8e...</span>\r\n </div>\r\n </div>\r\n </div>\r\n </div>\r\n </div>\r\n\r\n <div class="block">\r\n <input id="remember_me" type="checkbox" name="remember_me" onkeydown="check_enter(event)" /><label for="remember_me" onkeydown="check_enter(event)">\xe4\xb8\x8b\xe6\xac\xa1\xe8\x87\xaa\xe5\x8a\xa8\xe7\x99\xbb\xe5\xbd\x95</label>\r\n </div>\r\n <div class="block">\r\n <input type="submit" id="signin" class="button" value="\xe5\x8a\xa0\xe8\xbd\xbd\xe4\xb8\xad..." /> <span id="tip_btn" class="tip"></span>\r\n </div>\r\n <div class="block nav">\r\n » <a href="/register.aspx?ReturnUrl=http://i.cnblogs.com/" title="\xe6\xb3\xa8\xe5\x86\x8c\xe6\x88\x90\xe4\xb8\xba\xe5\x8d\x9a\xe5\xae\xa2\xe5\x9b\xad\xe7\x94\xa8\xe6\x88\xb7">\xe7\xab\x8b\xe5\x8d\xb3\xe6\xb3\xa8\xe5\x86\x8c</a><br />\r\n » <a href="http://www.cnblogs.com/ContactUs.aspx">\xe5\x8f\x8d\xe9\xa6\x88\xe9\x97\xae\xe9\xa2\x98</a>\r\n </div>\r\n </form>\r\n <div style="clear: both" />\r\n </div>\r\n </div>\r\n </div>\r\n</body>\r\n</html>\r\n'
>>>

我们爬取完网站后，得到的是一堆二进制码。按照正常的流程，浏览器从服务器端得到信息后会进行解析，然后展示给我们看。而我们现在可以通过简单的decode()命令将网页的信息进行解码，并显示出来，更新代码为：

from urllib import request

if __name__=="__main__":

    response=request.urlopen("http://i.cnblogs.com")

    html=response.read()

    html = html.decode("utf-8")

    print(html)

展示为:

Python 3.6.3 (v3.6.3:2c5fed8, Oct 3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>>
RESTART: C:\Users\DELL\AppData\Local\Programs\Python\Python36\urllib_test01.py

<!DOCTYPE html>

<html>

<head>

var return_url = 'http://i.cnblogs.com/';

var ajax_url = '/user' + '/signin';

var enable_captcha = false;

var is_in_progress = false;

</script>

</head>

您的浏览器未启用Javascript，无法进行登录。

</div>

<style>

form {

display: none;

}

</style>

</noscript>

<div id="Heading">登录博客园 - 代码改变世界</div>

<label class="label-line">登录用户名(<a href="/GetUsername.aspx" tabindex="-1" class="tb_right">找回</a>)</label>

</div>

</div>

<button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">×</span><span class="sr-only">Close</span></button>

请完成人机识别验证

</h4>

</div>

<span id="geetestLoading"> 验证码组件加载中,请稍后...</span>

</div>

<input id="remember_me" type="checkbox" name="remember_me" onkeydown="check_enter(event)" /><label for="remember_me" onkeydown="check_enter(event)">下次自动登录</label>

</div>

</div>

» <a href="/register.aspx?ReturnUrl=http://i.cnblogs.com/" title="注册成为博客园用户">立即注册</a><br />

» <a href="http://www.cnblogs.com/ContactUs.aspx">反馈问题</a>

</div>

</form>

</div>

</body>

</html>

自动获取网页编码方式的方法

安装第三方库chardet，它是用来判断编码的模块，打开cmd，只需要输入指令：

pip install chardet

即可进行下载。

新的代码：

# -*- coding: UTF-8 -*-

from urllib import request

import chardet

if __name__ == "__main__":

    response = request.urlopen("http://i.cnblogs.com/")

    html = response.read()

    charset = chardet.detect(html)

    print(charset)

返回的结果是一个字典，会告知我们网页的编码方式。