Generating prime numbers in chunks

prime_numbers.py

def extend(old, new):
    for p in old:
        cand = []
        for n in new:
            if n % p != 0:
                cand.append(n)
        if not cand:
            return old
        old.append(cand[0])
        new = cand[1:]

extend([2], range(3, 10)) # [2, 3, 5, 7]