Author Zed A. Shaw makes a simple promise in his Hard Way series of books from publisher Addison-Wesley Professional: "It'll be hard at first. But soon, you'll just get it—and that will feel great!" ...

If the argument is an expression (formula) it will evaluate it first. I don't do python3, but i imagine the python 2 "print x, y" command corresponds to "python (x,y)" if you want to think of it that ...