According to Dropbox, in 2011, when van Rossum first met Dropbox CEO Drew Houston, the Dropbox server and desktop client were written "almost exclusively in Python".
Today, Dropbox also relies on Go, TypeScript, and Rust, as well as the open source Mypy static type checker that Dropbox develops to manage Python code at scale. Mypy helps developers overcome the challenge of understanding dynamically typed Python code written by other developers in the past.
"There was a small number of really smart, really young coders who produced a lot of very clever code that only they could understand," said van Rossum. "That is probably the right attitude to have when you're a really small startup."
However, as Dropbox notes, when the company grew, new engineers could not understand the clever but 'short and cryptic' code written by and for earlier developers.
Van Rossum called this "cowboy coding culture" and educated the company about the value of maintainable code.
"When asked, I would give people my opinion that maintainable code is more important than clever code," he said.
"If I encountered clever code that was particularly cryptic, and I had to do some maintenance on it, I would probably rewrite it. So I led by example, and also by talking to other people."
Dropbox also credits van Rossum with sharpening the company's testing processes for its continuous integration program and helping engineers understand why tests were broken.
After that he started work on the Mypy static checker, which was written by Dropbox employee Jukka Lehtosalo, who van Rossum introduced to Dropbox. Van Rossum formed the mypy team in 2015 to help clean up Dropbox's massive Python codebase.
He also worked to make the engineer culture at Dropbox and in the Python community more inclusive for women, according to Dropbox.
"It's been an amazing ride to see this little hack of mine affect so many people in their lives," said van Rossum