Advent of Code is an Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like. People use them as a speed contest, interview prep, company training, university coursework, practice problems, or to challenge each other.
I've been doing this for the last three years and always with a different language. I'll note that I hardly ever finish all of them as other things occupy my time as well, but I find a lot of joy in tackling them.
This year, 2020, I'm doing it in Rust, the most loved programming language in Stack Overflow's annual developer survey. I'm currently learning and using it at my place of employment. It has been the most challenging programming language for me to learn so far, even though there are a ton of familiar ideas and concepts borrowed from some of my favorite languages. Forgive my slow pace :)
I have a python/ directory in this repo that includes Python 3 solutions as well and only attempt them because I'm stumped with working it out in Rust and want to determine a procedure or algorithm that works before porting it to Rust