展平嵌套序列

需求：将[1, 2, [3, 4, [5, 6], 7], 8]按顺序输出：1 2 3 4 5 6 7 8。
可以编写如下代码：

from collections import Iterable

def flatten(items, ignore_types=(str, bytes)):
    for x in items:
        if isinstance(x, Iterable) and not isinstance(x, ignore_types):
            yield from flatten(x)
        else:
            yield x

items = [1, 2, [3, 4, [5, 6], 7], 8]

# Produces 1 2 3 4 5 6 7 8
for x in flatten(items):
    print(x)