What do you need to pay attention to when designing web crawlers with
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"Web crawler", also known as web spider, is actually a kind of automated network robot, which replaces people to obtain information on the Internet. The business and strategy of many enterprises need a lot of multi-dimensional data analysis, which makes the crawler more and more popular. We need to pay attention to a few points to do a good job of the crawler. Let's take a look.
1, URL management and scheduling, if you want to access a lot of addresses, set up a URL manager to mark all the URL that need to be processed.
If the logic is not complex, you can use data structures such as arrays, which can be stored in a database when the logic is complex. One of the advantages of a database is that when a program hangs unexpectedly, it can continue to run based on the ID number being processed without having to start over and re-crawl the previously processed URL.
2. Data analysis, analysis data refers to the data needed in the content returned by the extraction server.
The original approach was to use "regular expressions", a general technique, and BeautifulSoup and Requests-HTML in Python are well suited for extracting content from tags.
3. Deal with anti-crawler strategy.
There are many strategies for the server to contain crawlers. Each HTTP request comes with a large number of parameters, and the server can determine whether the request is a malicious crawler based on the parameters. For example, the cookie value is incorrect and the server requires values other than Referer and User-Agent. At this time, we can see which values the server can accept through the browser, and then modify the various parameters of the request header in the code to pretend to be normal access.
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