[matusp]

The problem with this approach for me is that I don't know which variables are important outside of this snippet or outside of the next line. Is input_groups something I should keep in my head or is it just an intermediate result that can be discarded from my attention right away? The pipe-like solutions are nice because they are self-contained and you know that you only care about the final result and can abstract away the implementation.

I prefer python comprehensions for the same reason. I can tell that they are about crating a list or a dict and I don't need to parse a bunch of operations in a loop to come to the same conclusion.