examples of finding primes using filter in Liao Xuefeng"s Python tutorial are not clear,

def _odd_iter():
    n = 1
    while True:
        n = n + 2
        yield n

def _not_divisible(n):
    return lambda x: x%n > 0

def primes():
    yield 2
    it = _odd_iter();
    while True:
        n = next(it)
        yield n
        it = filter(_not_divisible(n), it) -sharp
for n in primes():
    if n < 30:
        print(n)
    else:
        break

about the sentence it = filter (_ not_divisible (n), it) , since it is an iterator that is lazily calculated, then every time filter runs to this sentence, filter only Filter a value from the current yield of the infinite list represented by it, so why do you end up with an infinite list that passes all the filters?