它是python自带的HTTP请求库

1）urllib.request：请求库

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

#参数意义：
#url:请求的链接
#data:post时用的请求
#[timeout]*超时时间
#后面的都是关于CA（证书）认证的选项

example:
a) get方法获取：

import urllib.request

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

b) post方法获取：

1. 先建立data对象
2. 使用bytes与urllib.parse建立可以用在urlopen中的data


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())

c)超时(timeout)功能使用：

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('TIME OUT')

d) 将url与data(表单)分离
使用request.Request()封装请求对象

from urllib import request,parse

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

e)add_header（）方法

from urllib import request,parse

url = 'http://httpbin.org/post'
dict = {
    'name':'Kim'
}
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 = urllib.request.urlopen(req)
print(response.read().decode('utf-8'))

Handler高级操作：通过urllib.request.build_opener(handler)来使用handler发送请求。

a) 代理设置：若遇到爬取网站限制同一IP访问时就需要代理来绕过限制：

1. 用urllib.request.ProxyHandler()封装代理对象
2. 将proxy_handler对象通过urllib.request.build_opener()函数来封装为代理对象
3. 使用 代理对象.open()方法打开目标链接。

import urllib.request

proxy_handler = urllib.request.ProxyHandler({
    'http':'http://180.125.137.126:8000',
    'https':'http://106.112.169.216:808'
})
opener = urllib.request.build_opener(proxy_handler)
try:
    response = opener.open('http://httpbin.org/get')
except urllib.error.URLError as e:
    if isinstance(e.reason,socket.timeout):
        print('TIME OUT')
print(response.read().decode('utf-8'))

b) 对于Cookie的操作：看到需要登陆才能看到的页面

使用导入的http.cookiejar
1. http.cookiejar.MozillaCookieJar()获取火狐浏览器格式的cookie
2. urllib.request.HTTPCookieProcessor()制作handler
3. 使用urllib.request.build_opener()来创建opener
4. 使用opener.open()
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)

-------------------------------------------------------------------------------------
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)

-------------------------------------------------------------------------------------
引入文件中的cookie并将其导入到请求中（cookie.load）
import http.cookiejar,urllib.request

cookie = http.cookiejar.MozillaCookieJar()
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'))

2）urllib.error：获取错误，保持爬虫程序的健壮。

*先HTTPError后URLError

from urllib import request,error

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

try:
    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')

3）urllib.parse：url的解析模块（URL拆分）

from urllib.parse import urlparse

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

输出：ParseResult(scheme='https', netloc='', path='www.baidu.com/index.html', params='user', query='id=5', fragment='comment')

urlunparse:

from urllib.parse import urlunparse

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


输出：http://www.baidu.com/index.html;user?a=6#comment

urljoin：

from urllib.parse import urlencode

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


输出：http://www.baidu.com?name=germey&age=22