I have been using python like this for over two decades. In fact these days I almost never write Python programs themselves, not liking the language much at all anymore. But I still habitually fire up Python to do calculations.

I may switch to Julia, though. I really prefer the language. Wish I could use it at work.

I used to use Python REPL for that until I switched to fish shell. Now I just run

    $ math "999.999 / 3"
    333.333

Granted, I don't really do any complex calculations in my terminal.

> Granted, I don't really do any complex calculations in my terminal.

Same. I use insect — https://github.com/sharkdp/insect

Python is great, but if you quickly want to play with matrices and vectors, then it’s a no-go