How to Write a Scrapy Spider Using Twisted

Scrapy is a Python web-crawling framework that allows developers to crawl a website and extract data from it. It’s written using Twisted, a popular event-driven networking framework that supports asynchronous execution.

It’s a high-performance, highly customisable web-crawling framework that comes with a large community of developers creating extensions & plugins for it. The vanilla version of Scrapy has everything you need to scrape and process web pages, but if that’s not enough then it’s easy to extend the system with open-source middlewares or your own plugins.

The scrapy stack consists of the engine (represented by the dark blue bar between ENGINE and DOWNLOADER in the figure above), Downloader, Scheduler and Spiders which each work in different ways to make your Scrapy system perform like a real-life web scraping robot. The engineĀ controls the data flow between all components of the system and triggers events when certain actions occur. The Downloader is responsible for downloading the webpages, generating responses and sending them back to the engine. The Spiders are the user-written classes which parse and extract items from those responses, generate requests, if needed, and send them to the engine.

Using the Spider class

You can write any type of spider you want in Scrapy, from simple spiders that follow links and collect data to complex crawlers that follow more tags and search results. Each spider has a class that you define, which tells the crawler where to start crawling, types of requests to make and how to parse data. It also has a parse function that is called whenever a response is received from the spider.

When writing a spider you must create a class with a unique name that defines what the spider should do and how it should work. This class must contain a list of URLs that the spider should start from, allow_domains which allows the spider to crawl only one domain and parse(self, response) which is the default callback function when the spider receives a response from a page it crawled.

There are several ways to use the parse function in a spider:

The first way is to pass a string of text as the response object. The second way is to use a XPath or CSS selector that identifies the identifier of the element on the web page that you want to extract data from.

Another way to parse a response is to take a variable that represents the value of the identifier of the element you want to extract information from and pass it as the response object. This is a great way to keep your code clean and concise and only include the information that you need.

Choosing the right tool

A powerful and user-friendly framework is the key to success when automating tasks. The framework you choose should be easy to implement, scalable, and have the power to handle larger tasks.

Scrapy is a Python web-crawling tool that helps you scrape and extract data from websites with ease. It comes with a variety of ways to get started, including the ability to scrape multiple pages in minutes, and support for all common data formats that you can input into other programs. It’s easy to learn, has great features and is loved by developers around the world.