对于找到的每个素数，将a filter应用于可迭代对象，所使用的过滤器是一项功能，它排除素数的所有倍数。

因此，您的可迭代项被包裹在与找到质数一样多的过滤器中，例如，排除了数字105，因为它可以被3整除，并且在找到质数3时添加了3的所有倍数的过滤器。

如果添加一些print语句，它将更加清晰（我希望）：

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

def _not_divisible(n):
    print('add filter for all multiples of', n)
    return lambda x: print('check if', x, 'is divisible by', n, 'result: ', not (x % n > 0)) or x % n > 0

def primes():
    yield 2
    it = _odd_iter()
    while True:
        n = next(it)
        yield n
        it = filter(_not_divisible(n), it)

for n in primes():
    if n < 20:
        print(n)
    else:
        break

打印：

2
3
add filter for all multiples of 3
check if 5 is divisible by 3 result:  False
5
add filter for all multiples of 5
check if 7 is divisible by 3 result:  False
check if 7 is divisible by 5 result:  False
7
add filter for all multiples of 7
check if 9 is divisible by 3 result:  True
check if 11 is divisible by 3 result:  False
check if 11 is divisible by 5 result:  False
check if 11 is divisible by 7 result:  False
11
add filter for all multiples of 11
check if 13 is divisible by 3 result:  False
check if 13 is divisible by 5 result:  False
check if 13 is divisible by 7 result:  False
check if 13 is divisible by 11 result:  False
13
add filter for all multiples of 13
check if 15 is divisible by 3 result:  True
check if 17 is divisible by 3 result:  False
check if 17 is divisible by 5 result:  False
check if 17 is divisible by 7 result:  False
check if 17 is divisible by 11 result:  False
check if 17 is divisible by 13 result:  False
17
add filter for all multiples of 17
check if 19 is divisible by 3 result:  False
check if 19 is divisible by 5 result:  False
check if 19 is divisible by 7 result:  False
check if 19 is divisible by 11 result:  False
check if 19 is divisible by 13 result:  False
check if 19 is divisible by 17 result:  False
19
add filter for all multiples of 19
check if 21 is divisible by 3 result:  True
check if 23 is divisible by 3 result:  False
check if 23 is divisible by 5 result:  False
check if 23 is divisible by 7 result:  False
check if 23 is divisible by 11 result:  False
check if 23 is divisible by 13 result:  False
check if 23 is divisible by 17 result:  False
check if 23 is divisible by 19 result:  False