爬虫基础：基本的urllib库

Urllib库是python内置的库

什么是Urllib

1. urllib.request 请求模块
2. urllib.error 异常处理模块
3. urllib.parse url解析模块
4. urllib.robotparser robots.txt解析模块

用法

• urlopen

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

GET类型的请求

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

POST类型的请求

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

带超时参数

response = urllib.request.urlopen('http://httpbin.org/get',timeout=1)
print(response.read())

测试较短的超时参数

import socket
import urllib.request
import urllib.error
try:
  response = urllib.request.urlopen('http://httpbin.org/get',timeout=0.1)
except urllib.error.URLError as e:
  if isinstance(e.reason,socket.timeout):
      print('TIMEOUT')
else:
  print('It is OK!')

查看urlopen返回值的类型

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

输出结果:<class 'http.client.HTTPResponse'>

响应内容--状态码和响应头

import urllib.request
response = urllib.request.urlopen('https://www.python.org')
print(response.status)
print(response.getheaders())
print(response.getheader('Server'))
print(response.read().decode('utf-8'))  #响应体，用utf-8解码

输出结果：
200
[('Server', 'nginx'), ('Content-Type', 'text/html; charset=utf-8'), ('X-Frame-Options', 'SAMEORIGIN'), ('x-xss-protection', '1; mode=block'), ('X-Clacks-Overhead', 'GNU Terry Pratchett'), ('Via', '1.1 varnish'), ('Content-Length', '48809'), ('Accept-Ranges', 'bytes'), ('Date', 'Sat, 18 Aug 2018 12:56:38 GMT'), ('Via', '1.1 varnish'), ('Age', '129'), ('Connection', 'close'), ('X-Served-By', 'cache-iad2128-IAD, cache-nrt6150-NRT'), ('X-Cache', 'HIT, HIT'), ('X-Cache-Hits', '2, 48'), ('X-Timer', 'S1534596999.663138,VS0,VE0'), ('Vary', 'Cookie'), ('Strict-Transport-Security', 'max-age=63072000; includeSubDomains')]
nginx

• request方法

如果使用复杂的请求可以在urlopen方法中使用request参数，通过构造request参数可以方便的设定请求的方式。

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

输出结果就是请求https://python.org的响应体。

使用POST方法发送请求，并用request构造函数构造request，作为参数调用urlopen

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

依然是使用POST方法发送请求，用Request构造函数构造request，作为参数传递给urlopen，但request中的headers不在构造函数中指定，而在使用request.add_header添加header。如果有很多键值对要传递，可以用for循环多次调用add_header

from urllib import request,parse
url = 'http://httpbin.org/post'
dict = {
      'name':'XieZ'
      }
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 -- urllib中的高级用法，代理、cookie等等各种高级功能都是各种handler实现的。

• 代理

import urllib.request
import urllib.request
proxy_handler = urllib.request.ProxyHandler({
  'http':'http://127.0.0.1:9743',
  'http':'https://127.0.0.1:9743'
  })
opener = urllib.request.build_opener(proxy_handler)
response = opener.open('http://www.baidu.com')
print(response.read())

• Cookie--Cookie可以用来保存登录会话信息

import http.cookiejar,urllib.request
cookie = http.cookiejar.CookieJar()
handler = urllib.request.HTTPCookieProcessor(cookie)
opener = urllib.request.build_opener(handler)
response = opener.open('http://www.baidu.com')
for item in cookie:
  print(item.name+"="+item.value)

把Cookie保存至文件，方便将来爬虫使用cookie登录网站，保持登录状态

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)

这样Cookie就保存在文件中了，MozillaCookieJar是cookiejar的子类，是火狐浏览器的cookie保存格式，还有其他的cookie保存格式，比如LWPCookieJar。在使用时，用什么格式保存就用什么格式读取cookie就行

 

使用LWPCookieJar将cookie保存到文件，并且读取此文件中的cookie，并请求页面

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)
mycookie = http.cookiejar.LWPCookieJar()
mycookie.load('cookie.txt',ignore_discard=True,ignore_expires=True)
handler = urllib.request.HTTPCookieProcessor(mycookie)
opener = urllib.request.build_opener(handler)
response = opener.open('http://www.baidu.com')
print(response.read().decode('utf-8'))

• urllib的异常处理模块

from urllib import request,error
try:
  response = request.urlopen('http://ljlhhljl.com/index.htm')
except error.URLError as e:
  print(e.reason)

结果显示：[Errno -2] Name or service not known

 

HTTPError含有reason、code、headers属性

from urllib import request,error
try:
  response = request.urlopen('http://www.sina.com.cn/99999.html')
except error.HTTPError as e:
  print(e.reason,e.code,e.headers,sep='
')
  print('This is end of HTTPError
')
except error.URLError as e:
  print(e.reason)
else:
  print('Request Sucessfully')

结果显示：

Not Found
404
Server: nginx
Date: Sun, 19 Aug 2018 22:06:25 GMT
Content-Type: text/html
Transfer-Encoding: chunked
Connection: close
Vary: Accept-Encoding
Age: 0
Via: http/1.1 ctc.nanjing.ha2ts4.77 (ApacheTrafficServer/6.2.1 [cMsSf ])
X-Cache: MISS.77
X-Via-CDN:     f=edge,s=ctc.nanjing.ha2ts4.65.nb.sinaedge.com,c=61.171.236.224;f=Edge,s=ctc.nanjing.ha2ts4.77,c=202.102.94.65
X-Via-Edge: 1534716385494e0ecab3d7c5e66ca3150b8e6

This is end of HTTPError

• URL解析模块--urlparse和urlunparse

1. urlparse函数

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

*返回结果：<class 'urllib.parse.ParseResult'> ParseResult(scheme='http', netloc='www.baidu.com', path='/index.html', params='user', query='id=5', fragment='comment')

2. urlunparse函数

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

*返回结果：http://www.baidu.com/index.html;user?a=6#comment
urlunparse就是urlparse的反函数，把各种参数拼接为一个url

3. urljpin函数

from urllib.parse import urljoin
print(urljoin('http://www.baidu.com','FAQ.html'))
print(urljoin('http://www.baidu.com','https://lllll.com/FAQ.html'))

*返回结果:http://www.baidu.com/FAQ.html
https://lllll.com/FAQ.html

4. urlencode--可以把字典对象转换成get请求参数，很常用

from urllib.parse import urlencode
params = {
      'name':'xiezheng',
      'age':23
      }
base_url = 'http://www.baidu.com?'
url = base_url + urlencode(params)
print(url)

*返回结果:http://www.baidu.com?name=xiezheng&age=23

• urllib.robotparser模块，用来解析robot.txt文件