Control flow and comprehensions

The shape most Python loops want to be

A very common loop creates an empty list, iterates, transforms, and appends. A comprehension expresses the same thing in one line that reads as a description of the result rather than a recipe for building it.

Comprehensions come in dict and set forms too, and a filtering clause folds the if into the same expression.

They stop helping when nested more than one level deep or when the expression grows a conditional inside a conditional. At that point an explicit loop is the readable choice, and readability is the entire point.