[igsomething]

They are different.

    def square_vals(x : list):
        return (val * val for val in x)

is a function that takes a list and returns a generator. While

    def square_vals(x : list):
        for val in x:
            yield val * val

is a generator itself.

The first case creates an anonymous generator. When in doubt you can always use the dis module: https://docs.python.org/3/library/dis.html