I obviously have a version without the memory issue.

The programming flexibility is indeed the win.

    def primes ():
        yield 2
        yield 3
        f = {}
        n = 5
        for p in primes():
            if p == 2:
                continue
            p2 = p*p
            while n < p2:
                if n in f:
                    double_p = f.pop(n)
                    m = n + double_p
                    while m in f:
                        m += double_p
                    f[m] = double_p
                else:
                    yield n
                n += 2
            f[n] = 2*p