What are crawlers used for?

The crawler program can be used to: 1. Obtain the source code of the web page; 2. Filter the data and extract useful information; 3. Save the data; 4. Analyze the data and conduct research; 5. Boost traffic and flash sales, etc. .

#The operating environment of this tutorial: Windows 7 system, Python 3 version, Dell G3 computer.

A web crawler (also known as web spider, web robot, more commonly known as web chaser in the FOAF community) is a program that automatically captures World Wide Web information according to certain rules or script. Other less commonly used names include ants, autoindexers, emulators, or worms.

The Internet is made up of hyperlinks. A link from one web page can jump to another web page. In the new web page, there are many links. Theoretically, starting from any web page and constantly clicking on links and links to linked web pages, you can travel throughout the entire Internet! Is this process like a spider crawling along a web? This is also the origin of the name "reptile".

In the process of understanding crawlers, due to the lack of systematic understanding of this technology, "newbies" will inevitably be dazzled and confused by the numerous and unfamiliar knowledge points. Some people plan to understand the basic principles and workflow first, some people plan to get started with the basic syntax of the software, and some people plan to understand the web page documents before starting... On the road to learning to capture network information, many people get lost halfway. Entering the trap will ultimately lead to failure. Therefore, it is indeed very important to master the correct method. Since crawlers are so powerful, what can the crawler program be used for?

Things that a web crawler program can do

1. Get a web page

Getting a web page can be simply understood as sending a network request to the server of the web page, and then The server returns the source code of our web page, in which the underlying principle of communication is relatively complex, and Python has encapsulated the urllib library and requests library for us. These libraries allow us to send various forms of requests very simply.

2. Extract information

The obtained web page source code contains a lot of information. If we want to extract the information we need, we need to further filter the source code. You can use the re library in python to extract information through regular matching, or you can use the BeautifulSoup library (bs4) to parse the source code. In addition to the advantage of automatic encoding, the bs4 library can also structure the source code information. Easier to understand and use.

3. Save data

After extracting the useful information we need, we need to save it in Python. You can use the built-in function open to save it as text data, or you can use a third-party library to save it as other forms of data. For example, it can be saved as common xlsx data through the pandas library. If there are unstructured data such as pictures, it can also be saved through the pymongo library. into an unstructured database.

4. Research

For example, you want to research an e-commerce company and want to know their product sales. The company claims monthly sales of hundreds of millions of dollars. If you use a crawler to crawl the sales of all products on a company's website, then you can calculate the company's actual total sales. Additionally, if you grab all the comments and analyze them, you can also find out if the site is being spammed. Data does not lie, especially massive data. Artificial falsification will always be different from what occurs naturally. In the past, it was very difficult to collect data with large amounts of data, but now with the help of crawlers, many deceptions will be nakedly exposed to the sun.

5. Brushing traffic and flash killing

Brushing traffic is a built-in function of the python crawler. When a crawler visits a website, if the crawler is well hidden and the website cannot recognize that the visit comes from a crawler, then it will be treated as a normal visit. As a result, the crawler "accidentally" swiped the website's traffic.

In addition to boosting traffic, you can also participate in various flash sales activities, including but not limited to grabbing products, coupons, air tickets and train tickets on various e-commerce websites. Currently, many people on the Internet exclusively use crawlers to participate in various activities and make money from them. This behavior is generally called "wooling", and such people are called "wool partyers". However, the act of using crawlers to "scrounge wool" for profit is actually a legal gray area, and I hope you will not try it.

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