def num():

    n = 1

    while True:

        n += 1

        yield n

def not_division(n):

    return lambda x: x % n > 0  #这里的x为it,但it是一个generator

def prime():

    it = num()

    while True:

        nn = next(it)

        yield nn

        it = filter(not_division(nn),it)

for n in prime():

    if n<1000:

        print(n)

    else:

        break