When using functional programming style, always use copious comments so the next poor sap who works on it knows what the magic one-liner does ;-)  (Alternatively, this Brian Kernighan quote often applies to functional programming or use of dunder variables in python: "Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?" :-)