딱히 의도한건 아니지만 메모삼아...

gistfile1.py

from collections import deque, Iterable
def flatten(l):
    """
    >>> [i for i in flatten([1, [2,3], [5, [6,7]]])]
    [1, 2, 3, 5, 6, 7]
    """
    queue = deque(l)
    while len(queue) > 0:
        p = queue.popleft()

        if isinstance(p, Iterable):
            for e in flatten(p):
                yield e
        else:
            yield p