Published: Fri 24 May 2024
By Chad Jemmett
In work .
tags: work algorithms
Depth-First Search for cataloging links on a site.
I briefly looked for some third-party tools, but I wanted to write up my own scraper. So I wrote up a little script to
do a depth-first search of all the site's links.
I've never used depth-first for any practical uses. Just searching and navigating test graphs. This was an actual
real-world application.
Tools
I used Python, Beautiful Soup , Deque , Requests and urllib.parse .
Beautiful soup I used to search the pages for a tags. Urllib.parse I used to pull the domain and directory from each
a tag. Deque was new to me. It's pronounced Deck and it's short for double end deque. It's part of the standard
Python library.
For each link, I used requests to get the html data.
deque is optimized for appending and popping at both ends of a List. A Pythonlist is similar butlistsare better for a fixed length in memory.dequeallows for more flexibility in thelist` length. For my purpose, list
would work just fine. The website I was scraping had roughly 1000 external links. But I enjoy learning about new aspects
of Python.
Deque was used to manage the stack data structure when doing a depth-first search. I used urllib.parse to figure
out what links were Google links and which links were not. I also used it to build up new links to add to the stack.
After some trial and error, I scraped all 70+ pages of our website and found nearly a thousand external links. Most
of them went to google as I figured, but a good percentage went to social media. It's satisfying to write a short
script to automate your way through hundreds of links to figure out what is what.
