So there probably aren't many circumstances where you would be choosing between one and the other, but one reason you might want to keep your eye on Rust is for

So there probably aren't many circumstances where you would be choosing between one and the other, but one reason you might want to keep your eye on Rust is for extension-writing. The traditional approach to dealing with stuff that needs to be fast in Python is to get it working in pure Python first, optimize as best you can, and if it's still not fast enough, profile to identify your hot loops and rewrite those bits in C as an extension. This is somewhat less necessary in the era of PyPy, but still a common way to think about things. To me, at least, Rust provides a compelling alternative to C in the Python+C combination. Coming from Python, writing C is pretty unergonomic; it's super-easy to shoot yourself in the foot and have your program die with an inexplicable segfault, which feels pretty alien for someone used to nice pretty stack traces. Rust promises to make that a lot more pleasant by being memory-safe, while still making good performance promises.