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This article mainly shows you "how to achieve a crawler", the content is easy to understand, clear, hope to help you solve doubts, the following let the editor lead you to study and learn "how to achieve a crawler" this article.

The first step is to determine the link to the crawled page

Since we usually crawl more than one page, we should pay attention to the changes in links when turning pages and keywords, sometimes even taking into account the date; in addition, the main web pages need to be statically and dynamically loaded.

Step 2 request resources

This is not difficult, mainly the use of the two Urllib,Request libraries, if necessary, you can flip through the official documents.

The third step is to parse the web page.

After the request for resources is successful, the source code of the entire web page is returned, and then we need to locate and clean the data. When it comes to data, the first point to pay attention to is the type of data, whether you should master it or not! Secondly, the data on the web page is often arranged neatly, thanks to the list, the use of most web data neat and regular, so lists, looping sentences should also be mastered! But it is worth noting that the web page data is not necessarily neat and regular, such as the most common personal information, except for the required options, I do not like to fill in other parts of the information, at this time some of the information is missing, you have to first judge whether there is data, and then crawl, so judge whether the sentence is not less! Mastering the above, our crawlers can basically run, but in order to improve code efficiency, we can use functions to divide a program into several small parts, each of which is responsible for part of the content. in this way, you can transfer a function many times as needed. If you are more powerful, if you develop a crawler software later, do you still need to master a class?

The fourth step is to save the data.

Do you have to open the file first, write the data, and finally close it, so you still have to master the reading and writing of the file?

Grasp the content that the reptile should learn, we will inevitably encounter anti-crawler problems, such as time limit, IP limit, CAPTCHA limit, and so on, may lead to the crawler can not be carried out, so there are many agents like Yiniuyun IP, time limit adjustment methods to contact the anti-crawler limit, of course, the specific operation methods need you to study.

The above is all the contents of the article "how to achieve a crawler". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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