Seven tips for Python to get started quickly

Chen Python 2020-11-16 17:09:00
tips python started quickly


There are also many reuse processes in the development process of crawlers , Here's a summary , We can save things in the future .

Multi person learning python, I don't know where to start .

Many people study python, After mastering the basic grammar , I don't know where to look for cases to start .

A lot of people who have done cases , But I don't know how to learn more advanced knowledge .

So for these three kinds of people , I will provide you with a good learning platform , Get a free video tutorial , electronic text , And the source code of the course !??¤

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1、 Basic Web Capture

get Method

post Method

2、 Using agents IP

In the process of developing crawlers, we often encounter IP The situation of being sealed off , At this point, you need to use an agent IP;

stay urllib2 There is... In the bag ProxyHandler class , Through this class, you can set up a proxy to visit a web page , The following code snippet :

3、Cookies Handle

cookies It's some websites to identify users 、 Conduct session Tracking data stored on the user's local terminal ( Usually encrypted ),python Provides cookielib Module for processing cookies,cookielib The main function of the module is to provide storage cookie The object of , To facilitate urllib2 Module to access Internet resources .

code snippet :

The key lies in CookieJar(), It is used for management HTTP cookie value 、 Storage HTTP Request generated cookie、 Outgoing to HTTP Request add cookie The object of . Whole cookie All stored in memory , Yes CookieJar After garbage collection of instance cookie Will also be lost , All processes do not need to be operated separately .

Manually add cookie:

4、 Pretend to be a browser

Some websites dislike the visit of reptiles , So I refused all requests to the reptiles . So use urllib2 Direct access to websites often appears HTTP Error 403: Forbidden The situation of .

Yes, some header Pay special attention ,Server The end will focus on these header Checking :

1.User-Agent There are some Server or Proxy The value will be checked , It is used to determine whether it is initiated by the browser Request.

2.Content-Type In the use of REST Interface ,Server The value will be checked , Used to determine HTTP Body How to analyze the content in .

At this time, you can modify http In bag header To achieve , The code snippet is as follows :

5、 Processing of verification code

For some simple verification codes , Simple identification . We've only done some simple captcha recognition , But there are some anti human captcha , such as 12306, Manual coding can be carried out through the coding platform , Of course, it's a fee .

6、gzip Compress

Have you met some webpages , No matter how to transcode, it's a mess . ha-ha , That means you don't know much web The service has the ability to send compressed data , This can reduce the amount of data transmitted on the network line 60% above . This is especially true for XML web service , because XML data The compression ratio of can be very high .

But the general server will not send compressed data for you , Unless you tell the server that you can handle compressed data .

So you need to change the code like this :

This is the key : establish Request object , Add one Accept-encoding The header tells the server that you can accept it gzip compressed data .

And then decompress the data :

7、 Multithreading concurrent fetching

If single thread is too slow , You need to multithread , Here is a simple thread pool template This program just prints 1-10, But it can be seen that it is concurrent .

Although I say Python Multithreading is a chicken bone , But for crawlers, the network frequency , It can improve efficiency to a certain extent .

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