snippet.sc

from itertools import islice
from time import time

def after(n=0):
    while 1:
        n += 1
        yield n
        
def filter_factors(n, g):
    while 1:
        x = g.next()
        if x % n:
            yield x

def primes():
    g = after(1)
    while 1:
        x = g.next()
        g = filter_factors(x, g)
        yield x

start = time()
print list(islice(primes(), 0, 498))
print time() - start