Being extremely pedantic, omitting the outer ()s is legal for a generator comprehension. That is, the following are equivalent:
foo(x for x in xs)
foo((x for x in xs))
gen = (x for x in xs)
foo(gen)
But these are not the same as:
foo([x for x in xs]
lst = [x for x in xs]
foo(lst)
It doesn't matter in this tiny example, but the difference between generators and lists can be very very important when working on very large amounts of data (e.g. processing a big text corpus), or a potentially-infinite stream of data.
