Dropbox is one of the most popular desktop applications in the world: You can install it today on Windows, macOS, and some flavors of Linux. What you may not know is that much of the application is written using Python. In fact, Drew’s very first lines of code for Dropbox were written in Python for Windows using venerable libraries such as pywin32.
Though we’ve relied on Python 2 for many years (most recently, we used Python 2.7), we began moving to Python 3 back in 2015. This transition is now complete: If you’re using Dropbox today, the application is powered by a Dropbox-customized variant of Python 3.5. This post is the first in a series that explores how we planned, executed, and rolled out one of the largest Python 3 migrations ever.