def flat_list(array):
    return iter(flat_iter(array))


def flat_iter(array):
    new_array = []
    for i in array:
        if hasattr(i, '__next__'):
            new_array += flat_iter(i)
        else:
            new_array.append(i)
    return new_array


if __name__ == '__main__':
    res = flat_list([1, 2, 3])
    assert hasattr(res, '__iter__'), "your function should return the iterator object"
    assert hasattr(res, '__next__'), "your function should return the iterator object"

    assert list(flat_list(iter([1, 2, 3]))) == [1, 2, 3], "First"
    assert list(flat_list(iter([1, iter([2, 2, 2]), 4]))) == [1, 2, 2, 2, 4], "Second"
    assert list(flat_list(iter([iter([2]), iter([4, iter([5, 6, iter([6]), 6, 6, 6]), 7])]))) == [2, 4, 5, 6, 6, 6, 6,
                                                                                                  6, 7], "Third"
    assert list(flat_list(iter([-1, iter([1, iter([-2]), 1]), -1]))) == [-1, 1, -2, 1, -1], "Four"
    print('Done! Check it')