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Python学习之旅（二十八）

2018-12-09 11:21:43来源：博客园阅读 ()

Python基础知识（27）：常用内建模块（Ⅲ）

1、urlblib

urllib提供了一系列用于操作URL的功能

url是统一资源定位符，对可以从互联网上得到的资源的位置和访问方法的一种简洁的表示，是互联网上标准资源的地址

互联网上的每个文件都有一个唯一的URL，它包含的信息指出文件的位置以及浏览器应该怎么处理它

（1）GET

urllib的request模块可以非常方便地抓取URL内容，也就是发送一个GET请求到指定的页面，然后返回HTTP的响应

#对豆瓣的一个URLhttps://api.douban.com/v2/book/2129650进行抓取，并返回响应
from urllib import request
with request.urlopen('https://api.douban.com/v2/book/2129650') as f:
    data = f.read()
    print('Status:', f.status, f.reason)
    for k, v in f.getheaders():
        print('%s: %s' % (k, v))
    print('Data:', data.decode('utf-8'))

结果：
Status: 200 OK
Date: Sun, 09 Dec 2018 01:23:48 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 2138
Connection: close
Vary: Accept-Encoding
X-Ratelimit-Remaining2: 99
X-Ratelimit-Limit2: 100
Expires: Sun, 1 Jan 2006 01:00:00 GMT
Pragma: no-cache
Cache-Control: must-revalidate, no-cache, private
Set-Cookie: bid=fdBz3SLSf0s; Expires=Mon, 09-Dec-19 01:23:48 GMT; Domain=.douban.com; Path=/
X-DOUBAN-NEWBID: fdBz3SLSf0s
X-DAE-Node: brand55
X-DAE-App: book
Server: dae
X-Frame-Options: SAMEORIGIN
Data: {"rating":{"max":10,"numRaters":16,"average":"7.4","min":0},"subtitle":"","author":["廖雪峰"],...}

如果我们要想模拟浏览器发送GET请求，就需要使用Request对象，通过往Request对象添加HTTP头，我们就可以把请求伪装成浏览器

#模拟iPhone 6去请求豆瓣首页
from urllib import request
req = request.Request('http://www.douban.com/')
req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
with request.urlopen(req) as f:
    print('Status:', f.status, f.reason)
    for k, v in f.getheaders():
        print('%s: %s' % (k, v))
    print('Data:', f.read().decode('utf-8'))

结果：
<title>豆瓣(手机版)</title>
        <meta name="google-site-verification" content="ok0wCgT20tBBgo9_zat2iAcimtN4Ftf5ccsh092Xeyw" />
        <meta name="viewport" content="width=device-width, height=device-height, user-scalable=no, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0">
        <meta name="format-detection" content="telephone=no">
        <link rel="canonical" href="
http://m.douban.com/">
        <link href="https://img3.doubanio.com/f/talion/4b1de333c0e597678522bd3c3af276ba6c667b95/css/card/base.css" rel="stylesheet">

（2）POST

如果要以POST发送一个请求，只需要把参数data以bytes形式传入

#模拟微博登录，先读取登录的邮箱和口令
from urllib import request, parse

print('Login to weibo.cn...')
email = input('Email: ')
passwd = input('Password: ')
login_data = parse.urlencode([
    ('username', email),
    ('password', passwd),
    ('entry', 'mweibo'),
    ('client_id', ''),
    ('savestate', '1'),
    ('ec', ''),
    ('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')
])

req = request.Request('https://passport.weibo.cn/sso/login')
req.add_header('Origin', 'https://passport.weibo.cn')
req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')

with request.urlopen(req, data=login_data.encode('utf-8')) as f:
    print('Status:', f.status, f.reason)
    for k, v in f.getheaders():
        print('%s: %s' % (k, v))
    print('Data:', f.read().decode('utf-8'))

结果：
Login to weibo.cn...
Email: email
Password: password
Status: 200 OK
Server: nginx/1.6.1
Date: Sun, 09 Dec 2018 02:01:40 GMT
Content-Type: text/html
Transfer-Encoding: chunked
Connection: close
Vary: Accept-Encoding
Cache-Control: no-cache, must-revalidate
Expires: Sat, 26 Jul 1997 05:00:00 GMT
Pragma: no-cache
Access-Control-Allow-Origin: https://passport.weibo.cn
Access-Control-Allow-Credentials: true
DPOOL_HEADER: 85-144-160-aliyun-core.jpool.sinaimg.cn
Set-Cookie: login=9da7cd806ada2c22779667e8e1c039c2; Path=/
Data: {"retcode":50011002,"msg":"\u7528\u6237\u540d\u6216\u5bc6\u7801\u9519\u8bef","data":{"username":"email","errline":669}}

（3）Handler

如果还需要更复杂的控制，比如通过一个Proxy去访问网站，我们需要利用ProxyHandler来处理

import urllib
proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
with opener.open('http://www.example.com/login.html') as f:
    pass

2、XML

操作XML有两种方法：DOM和SAX

DOM会把整个XML读入内存，解析为树，因此占用内存大，解析慢，优点是可以任意遍历树的节点

SAX是流模式，边读边解析，占用内存小，解析快，缺点是我们需要自己处理事件

正常情况下，优先考虑SAX，因为DOM实在太占内存

解析XML

在Python中使用SAX解析XML非常简洁，通常我们关心的事件是start_element，end_element和char_data，准备好这3个函数，然后就可以解析xml了

<a href="/">python</a> ……start_element读取<a href="/">，char_data读取Python，end_element读取</a>

from xml.parsers.expat import ParserCreate

class DefaultSaxHandler(object):
    def start_element(self, name, attrs):
        print('sax:start_element: %s, attrs: %s' % (name, str(attrs)))

    def end_element(self, name):
        print('sax:end_element: %s' % name)

    def char_data(self, text):
        print('sax:char_data: %s' % text)

xml = r'''<?xml version="1.0"?>
<ol>
    <li><a href="/python">Python</a></li>
    <li><a href="/ruby">Ruby</a></li>
</ol>
'''

生成XML

最简单也是最有效的生成XML的方法是拼接字符串

L = []
L.append(r'<?xml version="1.0"?>')
L.append(r'<root>')
L.append(encode('some & data'))
L.append(r'</root>')
return ''.join(L)

生成复杂的XML要用JSON

3、HTMLParser

利用HTMLParser，可以把网页中的文本、图像等解析出来

HTML本质上是XML的子集，但是HTML的语法没有XML那么严格，所以不能用标准的DOM或SAX来解析HTML。

好Python提供了HTMLParser来非常方便地解析HTML

from html.parser import HTMLParser
from html.entities import name2codepoint

class MyHTMLParser(HTMLParser):

    def handle_starttag(self, tag, attrs):
        print('<%s>' % tag)

    def handle_endtag(self, tag):
        print('</%s>' % tag)

    def handle_startendtag(self, tag, attrs):
        print('<%s/>' % tag)

    def handle_data(self, data):
        print(data)

    def handle_comment(self, data):
        print('<!--', data, '-->')

    def handle_entityref(self, name):
        print('&%s;' % name)

    def handle_charref(self, name):
        print('&#%s;' % name)

parser = MyHTMLParser()
parser.feed('''<html>
<head></head>
<body>
<!-- test html parser -->
    <p>Some <a href=\"#\">html</a> HTML&nbsp;tutorial...<br>END</p>
</body></html>''')

结果：
<html>


<head>
</head>


<body>


<!--  test html parser  -->

    
<p>
Some 
<a>
html
</a>
 HTML tutorial...
<br>
END
</p>


</body>
</html>