I hope that is never changed; I often write code in which the map function's results are very large, and keeping those around by default would cause serious memory consumption even when I am mapping over a sequence (rather than another generator).

Instead, I'd advocate the opposite extreme: Python makes it a little too easy to make sequences/vectors (with comprehensions); I wish generators were the default in more cases, and that it was harder to accidentally reify things into a list/tuple/whatever.

I think that if the only comprehension syntax available was the one that created a generator--"(_ for _ in _)"--and you always had to explicitly reify it by calling list(genexp) or tuple(genexp) if you wanted a sequence, then the conventions in the Python ecosystem would be much more laziness-oriented and more predictable memory-consumption wise.

Ah well, water under the bridge, I know.