I think that producing a list of tuples (that is conceptually image of mapping from some_iterable set) is basic operation. But... ok, now we have three ways to produce list below: [(f(x), f(x)) for x in some_iterable if f(x) < 2] 1)
def g(iterable): for x in iterable: y = f(x) if y < 2: yield (y, y)
2)
[(y, y) for y in (f(x) for x in some_iterable) if y < 2]
3)
map(lambda obj: (obj, obj), filter(lambda y: y < 2, map(f, some_iterable)))
And none of them does not look as obvious as [(f(x), f(x)) for x in some_iterable if f(x) < 2] , doesn't it? While proposed variant with where-clause [(y, y) for x in some_iterable if y < 2 where y = f(x)] looks more naturally than three suggested variants. I give strong emphasis on that fact, that where-clause is only syntactic sugar, suggested for better readability.