Python爬虫--Urllib库
Urllib库
Urllib是python内置的HTTP请求库,包括以下模块: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)
一、urllib.request 请求模块
1、urllib.request.urlopen
urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)
注: urlopen一般常用的有三个参数,它的参数如下:
urllib.requeset.urlopen(url,data,timeout)
1.1、url参数:
import urllib.request response = urllib.request.urlopen('http://www.baidu.com') print(response.read().decode('utf-8'))
1.2、data参数:
import urllib.parse import urllib.request data = bytes(urllib.parse.urlencode({'word': 'hello'}), encoding='utf8') print(data) response = urllib.request.urlopen('http://httpbin.org/post', data=data) print(response.read())
注:这里就用到urllib.parse,通过bytes(urllib.parse.urlencode())可以将post数据进行转换放到urllib.request.urlopen的data参数中。这样就完成了一次post请求。所以如果添加data参数的时候就是以post请求方式请求,如果没有data参数就是get请求方式
1.3、timeout参数
在某些网络情况不好或者服务器端异常的情况会出现请求慢的情况,或者请求异常,所以这个时候我们需要给请求设置一个超时时间,而不是让程序一直在等待结果
import urllib.request response = urllib.request.urlopen('http://httpbin.org/get', timeout=1) print(response.read())
1.4、响应类型、状态码、响应头
import urllib.request response = urllib.request.urlopen('https://www.python.org') print(type(response)) print(response.status) #获取状态码 print(response.getheaders().response.getheader("server")) #获取头部信息 print(response.read()) #获取响应体的内容
上述的urlopen只能用于一些简单的请求,因为它无法添加一些header信息,如果后面写爬虫我们可以知道,很多情况下我们是需要添加头部信息去访问目标站的,这个时候就用到了urllib.request
2、urllib.request.Request
2.1、request.Request 示例:
import urllib.request request = urllib.request.Request('https://python.org') response = urllib.request.urlopen(request) print(response.read().decode('utf-8'))
2.2、设置headers(请求头)
有很多网站为了防止程序爬虫爬网站造成网站瘫痪,会需要携带一些headers头部信息才能访问
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': 'QQ' } 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'))
通过add_header设置请求头:
from urllib import request, parse url = 'http://httpbin.org/post' dict = { 'name': QQ' } 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'))
2.3、设置代理
通过rulllib.request.ProxyHandler()可以设置代理,网站它会检测某一段时间某个IP 的访问次数,如果访问次数过多,它会禁止你的访问,所以这个时候需要通过设置代理来爬取数据
import urllib.request proxy_handler = urllib.request.ProxyHandler({ 'http': 'http://127.0.0.1:9743', 'https': 'https://127.0.0.1:9743' }) opener = urllib.request.build_opener(proxy_handler) response = opener.open('http://httpbin.org/get') print(response.read())
2.4、设置cookie
cookie中保存中我们常见的登录信息,有时候爬取网站需要携带cookie信息访问
import http.cookiejar, urllib.request cookie = http.cookiejar.CookieJar() #用于获取cookie以及存储cookie 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)
同时cookie可以写入到文件中保存,有两种方式http.cookiejar.MozillaCookieJar和http.cookiejar.LWPCookieJar()
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import http.cookiejar, urllib.request 2 filename = "cookie.txt" 3 cookie = http.cookiejar.MozillaCookieJar(filename) 4 handler = urllib.request.HTTPCookieProcessor(cookie) 5 opener = urllib.request.build_opener(handler) 6 response = opener.open('http://www.baidu.com') 7 cookie.save(ignore_discard=True, ignore_expires=True)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import http.cookiejar, urllib.request 2 filename = 'cookie.txt' 3 cookie = http.cookiejar.LWPCookieJar(filename) 4 handler = urllib.request.HTTPCookieProcessor(cookie) 5 opener = urllib.request.build_opener(handler) 6 response = opener.open('http://www.baidu.com') 7 cookie.save(ignore_discard=True, ignore_expires=True)
同样的如果想要通过获取文件中的cookie获取的话可以通过load方式,哪种方式写入的,就用哪种方式读取
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import http.cookiejar, urllib.request 2 cookie = http.cookiejar.LWPCookieJar() 3 cookie.load('cookie.txt', ignore_discard=True, ignore_expires=True) 4 handler = urllib.request.HTTPCookieProcessor(cookie) 5 opener = urllib.request.build_opener(handler) 6 response = opener.open('http://www.baidu.com') 7 print(response.read().decode('utf-8'))
二、urllib.error 异常处理模块
在很多时候我们通过程序访问页面的时候,有的页面可能会出现错误,类似404,500等错误,这个时候就需要我们捕捉异常:
1、URLError :reason属性,抓异常的时候只能打印错误信息
from urllib import request,error try: response = request.urlopen("http://pythonsite.com/1111.html") except error.URLError as e: print(e.reason)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import socket 2 3 from urllib import error,request 4 5 try: 6 response = request.urlopen("http://www.pythonsite.com/",timeout=0.001) 7 except error.URLError as e: 8 print(type(e.reason)) 9 if isinstance(e.reason,socket.timeout): 10 print("time out")
2、HTTPError(HTTPError是URLError的子类)里有三个属性:code,reason,headers
from urllib import request,error try: response = request.urlopen("http://pythonsite.com/1111.html") except error.HTTPError as e: print(e.reason) print(e.code) print(e.headers) except error.URLError as e: print(e.reason) else: print("reqeust successfully")
三、urllib.parse url解析模块
1、urlparse
将URL字符串拆分,然后以元组的形式展示。
from urllib.parse import urlparse result = urlparse("http://www.baidu.com/index.html;user?id=5#comment") print(result) #同时我们是可以指定协议类型: result = urlparse("www.baidu.com/index.html;user?id=5#comment",scheme="https") #这样拆分的时候协议类型部分就会是指定的部分,当然如果url里面已经带了协议,再通过scheme指定的协议就不会生效
2、urlunpars
将字符串拼接成url
from urllib.parse import urlunparse data = ['http','www.baidu.com','index.html','user','a=123','commit'] print(urlunparse(data))
3、urljoin
同样用于拼接字符串
from urllib.parse import urljoin print(urljoin('http://www.baidu.com', 'FAQ.html')) print(urljoin('http://www.baidu.com', 'https://pythonsite.com/FAQ.html')) print(urljoin('http://www.baidu.com/about.html', 'https://pythonsite.com/FAQ.html')) print(urljoin('http://www.baidu.com/about.html', 'https://pythonsite.com/FAQ.html?question=2')) print(urljoin('http://www.baidu.com?wd=abc', 'https://pythonsite.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'))
4、urlencode
这个方法可以将字典转换为url参数
from urllib.parse import urlencode params = { "name":"QQ", "age":12, } base_url = "http://www.baidu.com?" url = base_url+urlencode(params) print(url)