Pythonにおけるfilterの応用例−Etherふるい法による素数の求め

def _int_iter():#      3         
    n = 1
    while True:
        n = n + 2
        yield n
 
def  _not_divisible(n):#      
    return lambda x:x % n > 0
 
def primes():
    yield 2          #     2
    it = _int_iter() #     
    while True:
        n = next(it) #          
        yield n
        it = filter(_not_divisible(n), it) #      
for n in primes():#      ，               
    if n < 1000:
        print(n)
    else:
        break