I happen to prototype in python then move on to rust when things solidify... For those who don't know rust, its compiler is pretty slow. I mean, when you want to add a feature to an existing code base, each "run" you do to test the new feature imply relinking the whole project: that's very slow (or you have to split the project in sub project, but I'm lazy). In that situation, prototyping in python makes sense (at least to me :-)