What is a python crawler? Why is python called a crawler?

Today we will explain the basic conceptual knowledge of python. Many friends who are new to python have many questions. What is a python crawler? Then why is python called a crawler?

What is a python crawler?

Before entering the article, we first need to know what a crawler is. A crawler, that is, a web crawler, can be understood as a spider crawling on the Internet. The Internet is like a big web, and a crawler is a spider crawling around on this web. If it encounters its prey ( resources required), then it will grab it. For example, if it is crawling a web page, and it finds a path in this web, which is actually a hyperlink pointing to the web page, then it can crawl to another web page to obtain data. If it is not easy to understand, you can actually understand it through the following picture:

Because of the scripting characteristics of python, python is easy to configure. The processing of characters is also very flexible, and python has a rich network crawling module, so the two are often linked together. Python crawler development engineers start from a certain page of the website (usually the home page), read the content of the web page, find other link addresses in the web page, and then use these link addresses to find the next web page. This cycle continues until this Until all web pages of the website have been crawled. If the entire Internet is regarded as a website, then web spiders can use this principle to crawl all web pages on the Internet.

Crawlers can crawl the content of a website or application and extract useful value. You can also simulate user operations on browsers or App applications to implement automated procedures. The following behaviors can be achieved with crawlers:

vote-grabbing artifact

voting artifact

Prediction (stock market prediction , box office prediction)

National Sentiment Analysis

Social Relationship Network

As mentioned above, we can think that

crawlers generally refer to the crawling of network resources, and because Python's scripting features are not only easy to configure, but also very flexible in character processing. In addition, Python has rich web crawling modules, so the two are often linked together. This is why python is called a crawler.

Why is python called a crawler? As a programming language, Python is pure free software. It is deeply loved by programmers for its concise and clear syntax and forced use of whitespace characters for statement indentation. . To give an example: to complete a task, a total of 1,000 lines of code need to be written in C language, 100 lines of code in Java, and only 20 lines of code in Python. If you use Python to complete programming tasks, you will write less code, and the code will be concise, short, and more readable. When a team is developing, it will be faster to read other people's code, and the development efficiency will be higher, making the work more efficient.

This is a programming language that is very suitable for developing web crawlers, and compared to other static programming languages, Python’s interface for grabbing web documents is simpler; compared to other dynamic script languages, Python’s urllib2 package Provides a relatively complete API for accessing web documents. In addition, there are excellent third-party packages in python that can efficiently implement web page crawling, and can complete the tag filtering function of web pages with very short codes.

The structure of the python crawler is as follows:

##1. URL manager: manages the URLs to be crawled Collection and crawled URL collection, send the URL to be crawled to the web page downloader;

#2. Web page downloader: crawl the web page corresponding to the URL and store it as a string. Send it to the web page parser;

3. Web page parser: parse out valuable data, store it, and add the url to the URL manager.

The workflow of python is as follows:

(The Python crawler determines whether there is a URL to be crawled through the URL manager. If there is a URL to be crawled, it is passed to the downloader through the scheduler, the URL content is downloaded, and sent to the parser through the scheduler, the URL content is parsed, and the value data and new URL list are passed to the application through the scheduler, and the value is output Information process.)

Python is a programming language that is very suitable for developing web crawlers. It provides modules such as urllib, re, json, pyquery, etc., and it also has many established frameworks, such as Scrapy framework, PySpider crawler system, etc., which itself is very It is simple and convenient, so it is the preferred programming language for web crawlers! I hope this article can provide some help to friends who have just come into contact with the python language.

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