If you live in a major city, there’s a good chance you’ve used (or at least heard of) food delivery services like Postmates, GrubHub, or DoorDash. These services are great for times when I’m behind on groceries or when I’m getting some late night studying in before a big midterm or final. The only problem with these is that they’re not cheap. For a single order, the delivery fee and service fee can sometimes double the cost of the order.
Fortunately for me, Postmates regularly does promotions where they offer free food and waive the delivery fee for certain restaurants. The only problem with these promotions is that they’re easy to miss. I generally rely on waiting for a friend to catch one of these promotions by chance and text me about it. I actually have a group message with some friends titled “Free Postmates” that we exclusively use for keeping track of Postmates promotions.
I recently realized that I could make this process much simpler by creating something that would track the Postmates website and notify me of deals. In this post, I’ll describe how I built a tool to do this. It turned out to be a lot simpler than I had expected and has made me a lot more confident to create things like this in the future. If you’re new to the tools I use in this post, I hope that reading it helps you feel comfortable getting started with them!
Choosing a Language
Choosing a Web Scraper
This was a fairly easy decision as I had used Beautiful Soup for web scraping in Python before and had a good experience with it. Beautiful Soup isn’t the only option here, (another good one is Scrapy), but it’s the one I knew how to use and I knew that it would make things simple so I went with it.
Choosing a Notifier
The final thing I needed to decide on for this project was some way to notify myself when a promotion was found. I had been wanting to use Twilio for something for a while, so I decided to go with that. In case you haven’t heard of Twilio, it’s a service that provides a way to integrate different kinds of messaging into your program. One of it’s most popular features allows you to send and receive SMS messages. This seemed like a nice method since it wouldn’t require anything special on my phone.
When I’m working on something new like this, I like to start with the most basic steps and work my way up from there. For this project, that meant writing two separate super simple scripts: one that fetches the web page to scrape and just prints the whole thing, and one that sends a “Hello World” SMS to my phone.
After brushing up on the Beautiful Soup API, I came up with this:
from bs4 import BeautifulSoup import requests url = 'https://postmates.com/los-angeles' webpage = requests.get(url) soup = BeautifulSoup(webpage.text, 'html.parser') print(soup)
Not too impressive yet, but it’s always good to see something working before things get too complicated.
Now that I had the webpage, I wanted to get up and running with a basic “Hello World” through Twilio. They have a great Getting Started guide in their docs and it didn’t take long before I had received my first text from my free Twilio phone number.
from twilio.rest import TwilioRestClient account_sid = 'XXX' auth_token = 'XXX' twilio_phone_number = '+15558675309' my_phone_number = '+15551234567' client = TwilioRestClient(account_sid, auth_token) client.messages.create( body="Hello World!", to=my_phone_number, from_=twilio_phone_number )
After signing up for a free Twilio account and finding my account token, auth token, and registering a Twilio phone number, this worked like a charm!
Putting it all Together
Now that I had the basic pieces working, I just had to find a way to extract the promotions from the web page and connect it all up!
Fortunately for me, this turned out to be fairly simple as well.
After browsing the source for the front page of Postmates in my
developer console, I found out that whenever there is a free
<div> containing the restaurant’s title
also contained the word “Free”.1
This meant that all I needed to do was find the elements
containing the string “Free” and send their inner text to my phone!
This is what I ended up with:
from bs4 import BeautifulSoup import requests from twilio.rest import TwilioRestClient url = 'https://postmates.com/los-angeles' account_sid = 'XXX' auth_token = 'XXX' twilio_phone_number = '+15558675309' my_phone_number = '+15551234567' webpage = requests.get(url) soup = BeautifulSoup(webpage.text, 'html.parser') free_food = [s for s in soup.body.stripped_strings if 'free' in s.lower()] if free_food: body = 'Free Postmates!\n\n' + '\n'.join(free_food) client = TwilioRestClient(account_sid, auth_token) client.messages.create( body=body, to=my_phone_number, from_=twilio_phone_number )
And that’s it! The only thing left to do was to make this script run regularly enough to catch all the deals. This is the kind of thing that Cron is perfect for, but I had been reading a bit about Systemd Timers and how they can be used as an alternative to Cron jobs, so I chose to go with those. I won’t go into the details of setting up a Systemd Timer in this post, but I have some slides on it that provide a quick introduction in this post.
Thanks for reading this! I hope it helped provide insight into the way I approach creating something like this, and maybe even inspired you to make something similar. Feel free to comment if you have any questions about it, or if you notice anything that I could have done better.
edit: Since a few people have asked about this, I should point out that this script does end up sending the same text a lot if you have it running frequently. This was pretty annoying at first, so I ended up adding a way for it to log the current deals. I omitted it from this post for the sake of simplicity, but you can see the actual script that I am using here.
This has been the case with every free promotion I’ve seen so far, but it’s very possible that I’ve missed some if they follow a different format. ↩