Mostly-Benevolent Infection illustrates how one might spread new features to users of Khan Academy.

The main principle is to avoid giving different versions to users in the same classroom or with coaching relationships. Infection is illustrated through a simple web interface displaying the graph of users. This is not really a robust or friendly application, but rather a simple visualization! :)

The project could also have been implemented more easily completely in JavaScript, but I decided to put the infection logic in the server. Deciding when updates go out is best left to the people running the site.

Of course, real life would also be using Google Datastore, instead of in-memory processing!

In this guide, all commands are to be executed in the project root directory.

This app has been tested with Python 2.7.6 on Ubuntu 14.04 and Python 2.7.5 on OS X 10.9.5.

# Create a virtual-env for the app. Optional but recommended
virtualenv env; source env/bin/activate

# Install required packages
pip install -r requirements.txt

If either of these commands fail because they're not installed, here are guides for pip and virtualenv

nosetests

python main.py

The app should now be running at http://127.0.0.1:5000/

There are many approaches, but I took the greedy one, starting from a given user. The algorithm aims to minimize outgoing edges from the infected partition by expanding to nodes of low partition-leaving degree and high partition-internal degree first.

I expect a greedy expanding algorithm like this minimizes reads from the datastore. You don't need to figure out in advance what users in the population should be considered, and instead read each user as you go. Since this wasn't implemented with Datastore, it remains a theory!

Fun things to add with more time:

• user email shown on mouseover
• Some CSS for the page in general

Things that could use tweaking:

• Only one session at a time is supported (multiple tabs... not today!) via an ugly global variable
• The client-side JSX transformer is being used, and there's no compressing of JavaScript
• Tests don't extend to the web app section, or to limited_infect
• Limits on school and class sizes are not enforced
• I'm not familiar enough with how React re-renders to be braver in combining it withthe d3 postions. They're pretty separate right now, but it's not that way
• Infection status is tested based on 1ness or 2ness or the site_version. Too much hard-coding
• The logic of the react interface state is a bit convoluted and could use some more design work
• The entire list of infected nodes is transmitted on each infection. Should probably just be a diff!

Thanks to:

• MomsWhoThink.com for the adjectives and adverbs lists
• The United States Social Security Administration for the names list

The name generator gave these gems within the first 15 or 20 outputs. I am pleased:

• Malky.the.properly.scientific
• Janice.the.politely.aloof
• Adriel.the.unnecessarily.excited
• Myleigh.the.questioningly.demonic
• Christina.the.seldom.interesting