During Steve Huffman’s and Alexis Ohanian’s Pycon Keynote, someone asked why Reddit was moved from Lisp to Python. The reason for moving wasn’t too interesting, but why they have stayed is. Steve gave two “huge” reasons Reddit continues to use Python:

The biggest thing that has kept us on Python … well, there are two huge things. One are the libraries. There’s a library for everything. We’ve been learning a lot of these technologies and a lot of these architectures as we go. And, so, when I didn’t understand connection pools, I can just find a library until I understand it better myself and write our own. Don’t understand web frameworks, so we’ll use someone else’s until we make our own. Don’t understand a lot of stuff. And Python has an awesome crutch like that. And now, as we’ve been learning more, pulling more stuff back in house — just so we can have things the way we like them — it’s made the transition super super easy.

The other thing that keeps us on Python, and this is the major thing, is how readable and writable it is. When we hire new employees … I don’t think we’ve yet hired an employee who knew Python. I just say, “everything you write needs to be in Python.” Just so I can read it. And it’s awesome because I can see from across the room, looking at their screen, whether their code is good or bad. Because good Python code has a very obvious structure. And that makes my life so much easier. […] It’s extremely expressive, extremely readable, and extremely writable. And that just keeps life smooth.

The question gets asked around 25:54 on the video.