I am well aware that there are perfectly adequate ruby crawlers available to use, such RDig or Mechanize. Since the main idea is to learn while doing something fun and interesting and the best way to learn is to sometimes do things the hard way. I will examine all the different aspects of what makes a search engine the anatomy in a later post.
Please keep in mind that there are, of course, many resources for using resilient, well-tested crawlers in write a ruby webcrawler variety of languages. We have mere academic intentions here so we choose to ignore many important concerns, such as client-side rendering, parallelism, and handling failure, as a matter of convenience.
Traversing from the first page of the api directory, our crawler will visit web pages like a nodes of a tree, collecting data and additional urls along the way. Imagine that the results of our web crawl as a nested collection of hashes with meaningful key-value pairs.
If you choose to run this code on your own, please crawl responsibly. This will provide a familiar, flexible interface that can be adapted for logging, storage, transformation, and a wide range of use cases.
I want to simply ask a spider object for its results and get back an enumerator: Our Spider will maintain a set of urls to visit, data is collects, and a set of url "handlers" that will describe how each page should be processed.
Below is the enqueue method to add urls and their handlers to a running list in our spider. The processor will respond to the messages root and handler - the first url and handler method to enqueue for the spider, respectively.
The results method is the key public interface: The Enumerator class is well-suited to represent a lazily generated collection. While you could pass a block to consume the results, e. Returning an enumerator offers the potential to stream results to something like a data store.
Why not include Enumerable in our Spider and implement each instead? From Soup to Net Results Our Spider is now functional so we can move onto the details of extracting data from an actual website. Our processor, ProgrammableWeb will be responsible for wrappin a Spider instance and extracting data from the pages it visits.
As mentioned previously, our processor will need to define a root url and initial handler method, for which defaults are provided, and delegate the results method to a Spider instance: Our spider will invoke the handlers as seen above with processor.
Page docs providing a number of methods for interacting with html content: As data is collected, it may be passed on to handlers further down the tree via Spider enqueue.
Now we can make use of our ProgrammableWeb crawler as intended with simple instantiation and the ability to enumerate results as a stream of data: Skorks provided a straightforward, recursive solution to consume unstructured content.
Our approach is iterative and requires some work up front to define which links to consume and how to process them with "handlers".
However, we were able to achieve an extensible, flexible tool with a nice separation of concerns and a familiar, enumerable interface.
Modeling results from a multi-level page crawl as a collection may not work for every use case, but, for this exercise, it serves as a nice abstraction. It would now be trivial to take our Spider class and implement a new processor for a site like rubygems.
Try it yourself and let me know what you think of this approach full source. Share this post on Twitter Did you like this post? Stay in the LOOP!
Part of the Enumerable series. Published on Jan 27, Most Popular.How to write a simple web crawler in Ruby - revisited Crawling websites and streaming structured data with Ruby's Enumerator Let's build a simple web crawler in Ruby.
Covering Arizona's restaurants, resorts, travel activities and events with chef interviews, travel reviews, cocktails, recipes, and gardening tips. Throughout this article, we are going to use a text editor to write our todo list and our Ruby file.
The one we prefer at Codecademy is Sublime Text. If you don’t have a text editor like Sublime Text, read this article first to get it set up. Write your first web crawler in Python Scrapy Feb The scraping series will not get completed without discussing Scrapy.
In this post I am going to write . webcrawler; posted Oct 11, by Seema Siddique. Share this question Now, go read the gems documentation and try out the code. If you want to write a crawler yourself you could start with schwenkreis.com answer Oct 12, I need ruby equivalent code for this python script About Send feedback.
Many times when you're working with Ruby scripts you need to be able to write text information to a file. Writing text to a file with Ruby is reasonably straightforward. Just like many other languages, you need to open the file in "write" mode, write your data, and then close the file.