Tim> [Skip Montanaro] >> How much more expensive Tim> Stop right there. Okay, but I couldn't resist. ;-) >> for f in math.sin, math.cos, math.tan: >> squares = (f(x)**2 for x in inputs) >> plot(squares) Tim> Despite the similar appearance, that does something very different, ... >> which would work without reiterability, right? Tim> Yup. I shouldn't have mentioned performance. The above was really the point I was getting at. The mention of performance was simply because I couldn't understand why reiterability would be necessary in your example. I see you were just pointing out that someone not understanding the underlying nature of the generator would assume your example would work *and* save cycles because the definition of the generator expression was hoisted out of the loop. Skip