Python crawler from entry to abandonment (4) - basic usage of Urllib library 2

Others 2022-05-18 23:10:15 views: 0

Continue to learn the Urllib library from the previous content


response

Response type, status code, response headers

import urllib.request

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

You can see that the result is: <class 'http.client.httpresponse'="">
We can get the status code and header information response through response.status, response.getheaders().response.getheader("server")
. read() gets the content of the response body

Of course, the above urlopen can only be used for some simple requests, because it cannot add some header information. If we write a crawler later, we can know that in many cases, we need to add header information to access the target station, which is used at this time. urllib.request

request

There are many websites for setting Headers
. In order to prevent the website from being paralyzed by the program crawler, it is necessary to carry some header information to access it. The most common one is the user-agent parameter.

Write a simple example:

import urllib.request

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

Add header information to the request to customize the header information when you request the website

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': 'zhaofan'
}
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'))

The second way to add request headers

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'))

这种添加方式有个好处是自己可以定义一个请求头字典，然后循环进行添加

高级用法各种handler

代理,ProxyHandler

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())

cookie,HTTPCookiProcessor

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,这里用到了http.cookijar，用于获取cookie以及存储cookie

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)

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()，当然你自己用哪种方式都可以

具体代码例子如下：
http.cookiejar.MozillaCookieJar()方式

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)

http.cookiejar.LWPCookieJar()方式

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)

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，当然用哪种方式写入的，就用哪种方式读取。

import http.cookiejar, urllib.request
cookie = http.cookiejar.LWPCookieJar()
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

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，下面先写一个简单的例子

from urllib import request,error

try:
    response = request.urlopen("http://pythonsite.com/1111.html")
except error.URLError as e:
    print(e.reason)

上述代码访问的是一个不存在的页面，通过捕捉异常，我们可以打印异常错误

这里我们需要知道的是在urllb异常这里有两个个异常错误：
URLError,HTTPError，HTTPError是URLError的子类

URLError里只有一个属性：reason,即抓异常的时候只能打印错误信息，类似上面的例子

HTTPError里有三个属性：code,reason,headers，即抓异常的时候可以获得code,reson，headers三个信息，例子如下：

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")

同时，e.reason其实也可以在做深入的判断，例子如下：

import socket

from urllib import error,request

try:
    response = request.urlopen("http://www.pythonsite.com/",timeout=0.001)
except error.URLError as e:
    print(type(e.reason))
    if isinstance(e.reason,socket.timeout):
        print("time out")

URL解析

urlparse
The URL parsing functions focus on splitting a URL string into its components, or on combining URL components into a URL string.

urllib.parse.urlparse(urlstring, scheme='', allow_fragments=True)

功能一：

from urllib.parse import urlparse

result = urlparse("http://www.baidu.com/index.html;user?id=5#comment")
print(result)

结果为：

这里就是可以对你传入的url地址进行拆分
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你指定的部分，当然如果你的url里面已经带了协议，你再通过scheme指定的协议就不会生效

urlunpars

其实功能和urlparse的功能相反，它是用于拼接，例子如下：

from urllib.parse import urlunparse

data = ['http','www.baidu.com','index.html','user','a=123','commit']
print(urlunparse(data))

结果如下

urljoin

这个的功能其实是做拼接的，例子如下：

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'))

结果为：

从拼接的结果我们可以看出，拼接的时候后面的优先级高于前面的url

urlencode
这个方法可以将字典转换为url参数，例子如下

from urllib.parse import urlencode

params = {
    "name":"zhaofan",
    "age":23,
}
base_url = "http://www.baidu.com?"

url = base_url+urlencode(params)
print(url)

结果为：


原文地址：http://www.cnblogs.com/zhaof/p/6910871.html

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