greedy_flatten.py

test = [1, 2, 3, [4, 5], 6, 7, [8, [9, 10]], [[11, 12, [13, 14]]]]

def greedy_flatten(seq):
    if not isinstance(seq, list):
        return seq
    
    seq = seq.copy()
    while any([isinstance(x, list) for x in seq]):
        for idx, x in enumerate(seq):
            if isinstance(seq[idx], list):
                tmp = seq.pop(idx)
                flatten_tmp = greedy_flatten(tmp)
                for sub_idx, sub_x in enumerate(flatten_tmp):
                    seq.insert(idx+sub_idx, sub_x)

    
    return seq


def test_greedy_flatten():
    test = [1, 2, 3, [4, 5], 6, 7, [8, [9, 10]], [[11, 12, [13, 14]]]]
    
    assert greedy_flatten(test) == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
    assert test == [1, 2, 3, [4, 5], 6, 7, [8, [9, 10]], [[11, 12, [13, 14]]]]
    print('pass')

test_greedy_flatten()