Things i learn from scrapy

Early this month, I used scrapy to write spiders. And I won’t say that I use almost 2-3 hours to read the docs again, so I can get familiar with it for how it working.
But i just had written same code one year ago.
It’s just amazing how people often forget what they have done. And I think to write down the architecture of it would be a great thing for me, or for a better me. =)
So, how a spider work?
Let’s take a look at scrapy one.
There are 4 parts for Scrapy and a core engine in it.
In general, when you crawl a website, an index url is needed.
First, start the core Scrapy Engin, which is built on Twisted framework. It connects the 4 components and transfer messages in specific directions.
Second, we send the index url to Downloader, which download the page.
Then, the Spiders come in grape all the things you want, like link, images, content and so on. If the spider got new links, it just sends them to the Scheduler part, preparing for the next new crawling task.
By sending the new links to Scheduler, the Spiders part also send stuff like content to Item Pipeline.In the Item Pipeline part, raw content is being refactored and stored in db like MySQL.
So, what scrapy teaches me here?
One, try to split different parts to do only one thing.
Second, use middleware to extend the flexibility of your program.
Third, an architecture photo means a lot than words.