爬虫笔记：Urllib库详解

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爬虫第一课：爬虫的基本原理

什么是Urllib

Urllib是python 内置的http的请求库。包含四个模块

• urllib.request 请求模块
• urllib.error 异常处理模块
• urllib.parse url解析模块
• urllib.robotparser robots.txt解析模块（识别哪些网站可以爬）
  本文主要讲解前面三个模块

和python2中urlib模块区别

Python2
import urllib2
response = urllib2.urlopen(‘http://www.baidu.com’)

Python3
import urllib.request
response = urllib.request.urlopen(‘http://www.baidu.com’)

用法讲解

请求urlopen
urlopen

第一个参数URL请求网站，第二个参数data，post请求时需要，第三参数timeout限时设置，后面暂时用不到

#%% raw urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)

get请求网页打开

import urllib.requestresponse = urllib.request.urlopen('https://www.baidu.com/') print(response.read().decode('utf-8'))#解码

post请求网页打开

import urllib.request import urllib.parsedata = bytes(urllib.parse.urlencode({'word': 'hello'}), encoding='utf8')#编码 response = urllib.request.urlopen('http://httpbin.org/post', data=data) print(response.read())

timeout
设置一个超时时间，如果在规定时间没有完成请求，会报错

import urllib.requestresponse = urllib.request.urlopen('http://httpbin.org/get', timeout=0.1) print(response.read()) import socket import urllib.request import urllib.errortry:response = urllib.request.urlopen('http://httpbin.org/get', timeout=0.1) except urllib.error.URLError as e:if isinstance(e.reason, socket.timeout):print('TIME OUT')

响应

响应类型

import urllib.requestresponse = urllib.request.urlopen('https://www.python.org') print(type(response))

状态码和响应头
响应里面，包括两个重要信息：状态码和响应头

import urllib.requestresponse = urllib.request.urlopen('https://www.python.org') print(response.status)#状态码 print(response.getheaders())#响应头 print(response.getheader('Server'))#查看响应头具体某一项

读取响应read

#读取的响应为字节流型数据，需要解码为utf-8

import urllib.requestresponse = urllib.request.urlopen('https://www.python.org') print(response.read().decode('utf-8'))

Request
通过前面urlopen 我们可以请求一个网页并获取响应，但urlopen没法添加额外信息，如请求头，所以需要更高级的请求，Request

读取网页

import urllib.requestrequest = urllib.request.Request('https://python.org')#声明一个request对象 response = urllib.request.urlopen(request) print(response.read().decode('utf-8'))

添加请求头，同时post方式读取网页

from urllib import request, parseurl = 'http://httpbin.org/post' headers = {'User-Agent': 'Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)','Host': 'httpbin.org' } dict = {'name': 'Germey' } data = bytes(parse.urlencode(dict), encoding='utf8')#编码 req = request.Request(url=url, data=data, headers=headers, method='POST') response = request.urlopen(req) print(response.read().decode('utf-8'))

前面添加请求头是通过参数，还可以通过add_header方法

from urllib import request, parseurl = 'http://httpbin.org/post' dict = {'name': 'Germey' } data = bytes(parse.urlencode(dict), encoding='utf8') req = request.Request(url=url, data=data, method='POST') req.add_header('User-Agent', 'Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)') response = request.urlopen(req) print(response.read().decode('utf-8'))

Handler代理

import urllib.requestproxy_handler = urllib.request.ProxyHandler({'http': 'http://127.0.0.1:9743',#服务器网址'https': 'https://127.0.0.1:9743' }) opener = urllib.request.build_opener(proxy_handler) response = opener.open('http://httpbin.org/get') print(response.read())

Cookie
Cookie是在客户端保存的，用来记录用户身份的文本文件

如我们打开淘宝网页，左上角显示着用户名信息

审查元素，找到淘宝cookie，右键clear

刷新网页 用户登录信息消失

cookie如果有，可以维持用户登录信息，在做爬虫时，可以爬取一些登录后的信息。
1.打印cookie

import http.cookiejar, urllib.requestcookie = http.cookiejar.CookieJar()#声明cookie对象 handler = urllib.request.HTTPCookieProcessor(cookie) opener = urllib.request.build_opener(handler) response = opener.open('http://www.baidu.com/')#百度，我登录了百度账号 for item in cookie:print(item.name+"="+item.value) 2.保存cookie为文本文件

方式1

import http.cookiejar, urllib.request filename = "cookie.txt" cookie = http.cookiejar.MozillaCookieJar(filename) handler = urllib.request.HTTPCookieProcessor(cookie) opener = urllib.request.build_opener(handler) response = opener.open('http://www.baidu.com/') cookie.save(ignore_discard=True, ignore_expires=True)

方式2

import http.cookiejar, urllib.request filename = 'cookie.txt' cookie = http.cookiejar.LWPCookieJar(filename) handler = urllib.request.HTTPCookieProcessor(cookie) opener = urllib.request.build_opener(handler) response = opener.open('http://www.baidu.com/') cookie.save(ignore_discard=True, ignore_expires=True)

3.带cookie读取网页

import http.cookiejar, urllib.request cookie = http.cookiejar.LWPCookieJar()#要和前面保存方式一样 cookie.load('cookie.txt', ignore_discard=True, ignore_expires=True) handler = urllib.request.HTTPCookieProcessor(cookie) opener = urllib.request.build_opener(handler) response = opener.open('http://www.baidu.com/') print(response.read().decode('utf-8'))

异常处理

from urllib import request, error try:response = request.urlopen('http://cuiqingcai.com/index.htm') except error.URLError as e:print(e.reason) from urllib import request, errortry:response = request.urlopen('http://cuiqingcai.com/index.htm') except error.HTTPError as e:print(e.reason, e.code, e.headers, sep='\n') except error.URLError as e:print(e.reason) else:print('Request Successfully') import socket import urllib.request import urllib.errortry:response = urllib.request.urlopen('https://www.baidu.com', timeout=0.01) except urllib.error.URLError as e:print(type(e.reason))if isinstance(e.reason, socket.timeout):print('TIME OUT')

URL解析
urlparse
传入一个url，然后把一个url分割成几个部分。协议，域名，参数等

urllib.parse.urlparse(urlstring, scheme=’’, allow_fragments=True)

from urllib.parse import urlparseresult = urlparse('http://www.baidu.com/index.html;user?id=5#comment') print(type(result), result)

指定协议类型，传入的ur无协议

from urllib.parse import urlparseresult = urlparse('www.baidu.com/index.html;user?id=5#comment', scheme='https') print(result)

指定默认协议为ihttps，如果传入的url无协议就会被指定为https

from urllib.parse import urlparseresult = urlparse('http://www.baidu.com/index.html;user?id=5#comment', scheme='https') print(result)

锚点拼接allow_fragments

from urllib.parse import urlparseresult = urlparse('http://www.baidu.com/index.html;user?id=5#comment', allow_fragments=False)#allow_fragments锚点 print(result)

urlunparse：拼接URL

from urllib.parse import urlunparsedata = ['http', 'www.baidu.com', 'index.html', 'user', 'a=6', 'comment'] print(urlunparse(data))

urljoin

from urllib.parse import urljoinprint(urljoin('http://www.baidu.com', 'FAQ.html')) print(urljoin('http://www.baidu.com', 'https://cuiqingcai.com/FAQ.html')) print(urljoin('http://www.baidu.com/about.html', 'https://cuiqingcai.com/FAQ.html')) print(urljoin('http://www.baidu.com/about.html', 'https://cuiqingcai.com/FAQ.html?question=2')) print(urljoin('http://www.baidu.com?wd=abc', 'https://cuiqingcai.com/index.php')) print(urljoin('http://www.baidu.com', '?category=2#comment')) print(urljoin('www.baidu.com', '?category=2#comment')) print(urljoin('www.baidu.com#comment', '?category=2'))

urlencode
把字典对象转换为get请求参数

from urllib.parse import urlencodeparams = {'name': 'germey','age': 22 } base_url = 'http://www.baidu.com?' url = base_url + urlencode(params) print(url)

作者：电气-余登武。
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