爬虫笔记：Urllib库详解

如果不懂爬虫，请看链接
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.request

response = 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.parse

data = 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.request

response = urllib.request.urlopen('http://httpbin.org/get', timeout=0.1)
print(response.read())

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')

响应

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响应类型

import urllib.request

response = 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.request

response = 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.request

response = 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.request

request = 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, parse

url = '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, parse

url = '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.request

proxy_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.request

cookie = 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, 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')

import socket
import urllib.request
import urllib.error

try:
    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 urlparse

result = 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 urlparse

result = 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 urlparse

result = 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 urlparse

result = 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 urlunparse

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

urljoin

from urllib.parse import urljoin

print(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 urlencode

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

在这里插入图片描述
作者：电气-余登武。
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