Infinite list of primes! Yay!

or until the memory gives up...

# -*- coding: utf-8 -*-

from itertools import count
from collections import defaultdict

def seive():
    table = defaultdict(list)
    for x in count(2):
        facts = table[x]
        if facts:
            del table[x]
            for p in facts:
                table[x+p] = table[x+p] + [p]
        else:
            table[x*x] = [x]
            yield x
    
if __name__ == '__main__':
    for k, v in enumerate(seive()):
        print k, v

Got the idea from here.