#-*- coding:utf-8 -*-
#01.urllib2_urlopen.py
#导入urllib2库
import urllib2
#向指定的url发送请求，并返回服务器的类文件对象
response = urllib2.urlopen("http://www.baidu.com")
#类文件对象支持文件对象的操作方法，如read()方法读取文件
html = response.read()
#打印字符串
print(html)

python2 01.urllib2_urlopen.py 

urllib2.urlopen(url[, data[, timeout[, cafile[, capath[, cadefault[, context]]]]])
Open the URL url, which can be either a string or a Request object.

#-*- coding:utf-8 -*-
#02.urllib2_request.py

import urllib2

#url作为Request()方法的参数，构造并返回一个Request对象
request = urllib2.Request("http://www.baidu.com")

#Request对象作为一个urlopen()方法的参数，发送给服务器并接收响应
response = urllib2.urlopen(request)

html = response.read()

print(html)

#-*- coding:utf-8 -*-
#03.urllib2_useragent.py

import urllib2

url = "http://www.itcast.cn"

#IE 9.0的User-Agent,包含ua-header里
ua_header = {"User-Agent":"Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0;"}

# url连同headers,一起构造Request请求，这个请求将附带IE9.0浏览器的User-Agent
request = urllib2.Request(url, headers = ua_header)

#向服务器发送这个请求
response = urllib2.urlopen(request)

html = response.read()

print(html)

#-*- coding:utf-8 -*-
#04.urllib2_headers.py

import urllib2

url = "http://www.itcast.cn"

#IE 9.0的User-Agent
header = {"User-Agent":"Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0;"}
request =urllib2.Request(url, headers = header)

#也可以通过调用Request.add_header()添加/修改一个特定的header
request.add_header("Connection","keep-alive")

#也可以通过调用Request.get_header()来查看header信息
request.get_header(header_name = "Connection")

response = urllib2.urlopen(request)
print(response.code)  #可以查看响应状态码

html = response.read()
print(html)

  随机添加/修改User-Agent

#-*- coding:utf-8 -*-
#05.urllib2_add_headers.py

import urllib2
import random

url = "http://www.itcast.cn"

ua_list = [
  "Mozilla/5.0 (Windows NT 6.1; ) Apple.... ",
  "Mozilla/5.0 (X11; CrOS i686 2268.111.0)... ",
  "Mozilla/5.0 (Macintosh; U; PPC Mac OS X.... ",
  "Mozilla/5.0 (Macintosh; Intel Mac OS... "
]

user_agent = random.choice(ua_list)

request = urllib2.Request(url)

#也可以通过调用Request.add_header()添加/修改一个特定的header
request.add_header("User-Agent", user_agent)

#第一个字母大写，后面的全部小写
request.add_header("User-agent")

response = urllib2.urlopen(req)

html = response.read()

print(html)