Python

Generally I bash together the one-off programs in Python and if I discover that my "one off" program is actually being run 4 times a week, that's when I look at switching to a compiled language.

Case in point: I threw together a python program that followed a trajectory in a point cloud and erased a box around the trajectory. Found a python point cloud library, swore at my code (and the library code) for a few hours, tidied up a few point clouds with it, job done.

And then other people in my company also needed to do the same thing and after a few months of occasional use, I rewrote it using C++ and Open3D. A few days of swearing this time (mainly because my C++ is a bit rusty, and Open3D's C++ interface is a sparsely-documented back end to their main python front end).

End result though is that point clouds that took 3 minutes to process before in python now take 10 seconds, and now there's a visualisation widget that shows the effects of the processing so you don't have to open the cloud in another viewer to see that it was ok.

But anyway, like you said, python is good for prototyping, and when you hash out your approach and things are fairly nailed down and now you'd like some speed, jump to a compiled language and reap the benefits.