Lie Ryan schrieb:
I hate it. It mixes map/filter style and comprehension style; and the fact it does so in a single line only makes it worse. Not that it would be any better in two lines.
Taking this further, using only map/filter style like this
filter(pred, map(f, seq))
takes two steps. Why is it so bad that doing it in a listcomp
(el for el in (f(y) for y in seq) if el > 2)
takes two steps as well?
Georg
Comprehension, by its nature, is map+filter in a single expression.
Let's stick with "+" for function composition. Then comprehension is, as you say, ``map + filter`` (map after filter). It is *not* ``filter + map`` (filter after map), which is what would be needed in the case discussed in this thread. In the functional waym you can of course combine map and filter in the order you like.
Nested comprehension is (map+filter)+(map+filter).
Yes, and in this case, we use it as ``(id+filter) + (map+id)``, which is the easiest way to build a ``filter + map`` with the ``map + filter`` building block.
Mixing the two styles is ugly since it means you have to think in two separate (though related) paradigms.
I mentally translate map and filter into comprehensions anyway (or maybe rather both translate into the same more abstract thing), so I don't see it as ugly. Georg