gen_prime.py

#! /usr/bin/env /python
# -*- coding: utf-8 -*-

from itertools import ifilter, islice

def gen_odd():
    n = 3
    while True:
        yield n
        n += 2

def primes1():
    yield 2
    g = gen_odd()
    while True:
        prime = g.next()
        yield prime
        g = ifilter(lambda x, prime = prime: x % prime, g)

def primes3():
    yield 2
    g = gen_odd()
    while True:
        prime = g.next()
        s_prime = prime * prime
        ps = []
        while s_prime != prime:
            yield prime
            ps.append(prime)
            prime = g.next()
        pred = lambda x, ps = ps: all(x % p for p in ps)
        g = ifilter(pred, g)

def bench():
    from timeit import Timer
    import timeit
    timeit.__dict__.update(p1 = primes1)
    timeit.__dict__.update(p3 = primes3)
    stmt = 'for p in g: pass'
    setup1 = 'g = itertools.islice(p1(), MAX)'
    setup3 = 'g = itertools.islice(p3(), MAX)'
    for n in (100, 1000, 10000):
        timeit.__dict__.update(MAX = n)
        print 'take %d primes: %f : %f' % (n, Timer(stmt, setup1).timeit(1), Timer(stmt, setup3).timeit(1))

def test():
    MAX = 1000
    p1 = [p for p in islice(primes1(), MAX)]
    p3 = [p for p in islice(primes3(), MAX)]
    print p1 == p3, len(p1), len(p3)

if __name__ == u'__main__':
    #test()
    bench()

result.txt

take 100 primes: 0.001078 : 0.000558
take 1000 primes: 0.098870 : 0.008400
take 10000 primes: 9.724632 : 1.687156