Scrapy

Starting a project

scrapy startproject <project_name>

This creates a file structure like so:

├── scrapy.cfg
└── <project_name>
	├── __init__.py
	├── items.py
	├── middlewares.py
	├── pipelines.py
	├── settings.py
	└── spiders
		└── __init__.py

• settings.py is where project settings are contained, like activating pipelines, middlewares etc. You can change the delays, concurrency, and lots more things.
• items.py is a model for the extracted data. You can define a custom model (like a ProductItem) that will inherit the Scrapy Item class and contain your scraped data.
• pipelines.py is where the item yielded by the spider gets passed, it’s mostly used to clean the text and connect to file outputs or databases (CSV, JSON SQL, etc).
• middlewares.py is useful when you want to modify how the request is made and scrapy handles the response.
• scrapy.cfg is a configuration file to change some deployment settings, etc.

Spiders

Scrapy provides several different spider types. Some of the most common ones:

• Spider - Takes a list of start_urls and scrapes each one with a parse method.
• CrawlSpider - Designed to crawl a full website by following any links it finds.
• SitemapSpider - Designed to extract URLs from a sitemap

To create a new generic spider, run:

scrapy genspider <name_of_spider> <website>

A new spider will now have been added to your spiders folder, and it should look like this:

import scrapy
 
class NAMEOFSPIDERSpider(scrapy.Spider):
	name = 'NAMEOFSPIDER'
	allowed_domains = ['website']
	start_urls = ['website']
 
def parse(self, response):
	pass

This spider class contains:

• name - an attribute that gives a name to the spider. We will use this when running our spider
• allowed_domains - an attribute that tells Scrapy that it should only ever scrape pages of the <website> domain. This prevents the spider from going and scraping lots of websites. This is optional.
• start_urls - an attribute that tells Scrapy the first URL it should scrape.
• parse - this function is called after a response has been received from the target website.

To start using this Spider we will have to:

1. Change the start_urls to the URL we want to scrape
2. Insert our parsing code into the parse function

You run a spider with:

scrapy crawl <name_of_spider>

Scrapy Shell

scrapy shell

If we run

fetch(<start_url>)

we should see a 200 response in the logs. Scrapy will save the HTML response in an object called response

You can get a list of elements matching a CSS selector by running

response.css("<selector>")

To just get the first matching element run

response.css("<selector>").get()

This returns all the HTML in this node of the DOM tree.

CSS Selectors

Tags: Programming