Building An Image Crawler Using Python And Scrapy

Published Aug 01, 2017

Have you ever needed to pull data from a website that doesn’t provide an API? Well, you can just pull the data out from the HTML then! This tutorial will teach you how to scrape websites so that you can get the data you want from third party websites without using APIs.

Scrapy is an open source web scraping and crawling framework written in Python. We’ll learn how to use Scrapy to crawl and scrape websites.

Prerequisites

You should be comfortable with writing code in Python. You should also know how to use Regular Expressions(Regex). A great tutorial for learning Regex can be found on Regexone.

Installation

You need the following tools:

Windows users

Once you have installed both Python and Scrapy, make sure you have them in your PATH environment variable. Here is a detailed installation guide for both Python and Scrapy.

Creating a project

Once you’ve set up the above tools, you are ready to dive into creating a Crawler. Let's start by creating a Scrapy project. Fire up your terminal and enter:

$ scrapy startproject imagecrawler

This will create a directory for you with the following structure:

imagecrawler/ scrapy.cfg # deploy configuration file imagecrawler/ # project's Python module, you'll import your code from here __init__.py items.py # project items definition file pipelines.py # project pipelines file settings.py # project settings file spiders/ # a directory where you'll later put your spiders __init__.py

Building your first spider

Spiders are classes that you define and what Scrapy uses to scrape information from a website (or a group of websites). They must subclass scrapy.Spider and define the initial requests to make, optionally, how to follow links in the pages, and how to parse the response to extract data.

Create a new file called pexels\_scraper.py in the spiders folder with the following content:

import scrapy class PexelsScraper(scrapy.Spider): name = "pexels" def start_requests(self): url = "https://www.pexels.com/" yield scrapy.Request(url, self.parse) def parse(self, response): print response.url, response.body

Let's look at what the literals in the above code mean:

  • name: Identifies the Spider. You’ll use this name to start crawling.
  • start_requests(): Returns an iterable of Requests that’ll get executed.
  • parse(): Parses the response, extracting the scraped data as dicts and also finding new URLs to follow and creating new requests (Request) from them.

To run the code we've written above, open your terminal and cd to the imagecrawler directory and enter the following command:

$ scrapy crawl pexels

This will start the crawler and print the url and the body of the response it got back. Then the crawler will stop. This is because we haven’t yet specified how to move to links it encounters on a page. We’ll look at that in the next section.

Recursively crawling the website

Now that we’ve set up the project, let’s look at the website we’ll scrape. We’ll scrape Pexels, a website that provides high quality and completely free stock photos. They have an API but it has a limit of 200 requests per hour. We’ll crawl this website for images, url of the page we found them on and the tags associated with them.

Lets go to Pexels.com and open an image. Let us first examine the URL structure which is used by pexels for each image. It is of the form:

https://www.pexels.com/photo/cosmos-dark-galaxy-hd-wallpaper-173383/

All links containing photos have the following in common:

  • They start with https://www.pexels.com/photos/
  • They have an id at the end of the link: 173383

We’ll extract all links from the pages we visit. Then we’ll filter out all links that do not match the given prefix. We’ll use the id to keep track of the links we’ve already visited so that we do not crawl same pages repeatedly.

First import 3 modules we’ll need for the above tasks: re, LinkExtractor and Selector. Then we need a regex url matcher that’ll match the common url. We also need a function to extract image ids from urls. Modify the PexelScraper class so that it looks like the following:

import scrapy
import re
from scrapy.linkextractor import LinkExtractor
from scrapy.selector import Selector class PexelsScraper(scrapy.Spider): name = "pexels" # Define the regex we'll need to filter the returned links url_matcher = re.compile('^https:\/\/www\.pexels\.com\/photo\/') # Create a set that'll keep track of ids we've crawled crawled_ids = set() def start_requests(self): url = "https://www.pexels.com/" yield scrapy.Request(url, self.parse) def parse(self, response): body = Selector(text=response.body) link_extractor = LinkExtractor(allow=PexelsScraper.url_matcher) next_links = [link.url for link in link_extractor.extract_links(response) if not self.is_extracted(link.url)] # Crawl the filtered links for link in next_links: yield scrapy.Request(link, self.parse) def is_extracted(self, url): # Image urls are of type: https://www.pexels.com/photo/asphalt-blur-clouds-dawn-392010/ id = int(url.split('/')[-2].split('-')[-1]) if id not in PexelsScraper.crawled_ids: PexelsScraper.crawled_ids.add(id) return False return True

Looking at the website structure

We are now getting only the pages we wanted to get. We now want to get the image urls and associated tags for the images. For this, We need to take a look at how the HTML pages for images look. Go to an image page on pexels. Now right click on the image and click Inspect Element, you’ll see something like this:

img_class

We can see that the img tag has a class image-section__image. We’ll use this information to extract this tag. The url of the image is in the src attribute and the tags we need are there in the alt attribute. Now let us modify our PexelsScraper class to extract these things and print them out to the console.

For this we’ll create 2 regex patterns that’ll extract the src and alt attributes for us. Then we’ll use the css method in the Selector class to extract img tags with class image-section__image. Finally we’ll extract the url and tags and print them to the screen.

Add the following variables to the PexelsScraper class:

src_extractor = re.compile('src="([^"]*)"')
tags_extractor = re.compile('alt="([^"]*)"')

Now modify the parse method such that it prints the required url and tags:

def parse(self, response): body = Selector(text=response.body) images = body.css('img.image-section__image').extract() # body.css().extract() returns a list which might be empty for image in images: img_url = PexelsScraper.src_extractor.findall(image)[0] tags = [tag.replace(',', '').lower() for tag in PexelsScraper.tags_extractor.findall(image)[0].split(' ')] print img_url, tags link_extractor = LinkExtractor(allow=PexelsScraper.url_matcher) next_links = [link.url for link in link_extractor.extract_links(response) if not self.is_extracted(link.url)] # Crawl the filtered links for link in next_links: yield scrapy.Request(link, self.parse)

The body.css(‘img.image-section__image’).extract() call gives us all the img tags with class image-section__image in a list.

Now you can run the spider and test it out! Open your terminal and enter the following:

 $ scrapy crawl pexels

You’ll get the output similar to the following:

https://images.pexels.com/photos/132894/pexels-photo-132894.jpeg?w=940&h=650&auto=compress&cs=tinysrgb [u'red', u'and', u'grey', u'fish', u'on', u'ice']
https://images.pexels.com/photos/343812/pexels-photo-343812.jpeg?w=940&h=650&auto=compress&cs=tinysrgb [u'cuisine', u'delicious', u'diet']
https://images.pexels.com/photos/274595/pexels-photo-274595.jpeg?w=940&h=650&auto=compress&cs=tinysrgb [u'adult', u'beautiful', u'beauty']
https://images.pexels.com/photos/230824/pexels-photo-230824.jpeg?w=940&h=650&auto=compress&cs=tinysrgb [u'orange', u'squash', u'beside', u'stainless', u'steel', u'bowl']

Wrapping up

So in around 50 lines of code, we were able to get a web crawler( which scrapes a website for images) up and running. This was just a tiny example of something you could do with a web crawler. There are whole businesses running based on web scraping, for example, most of the product price comparison websites use crawlers to get their data.

Now that you have the basic knowledge of how to build a crawler, go and try building your own crawler!


This post was originally published by the author here. This version has been edited for clarity and may appear different from the original post.

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Webshare.io
2 months ago

If you are getting blocked by websites, you can use a free proxy with thousands of IP addresses for Scrapy at https://proxy.webshare.io/

Dave
3 months ago

This has taken my porn collection to the next level ;)

Ayush Gupta
3 months ago

Damn, never thought people would use scraping for that ;)

Kenneth Adeshina
3 months ago

yes this is really helpful

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