flat_list.py

def flatten(e):
    if isinstance(e, list):
        return flat_list(e)
    else:
        return [e]


def flat_list(array):
    return sum([flatten(x) for x in array], [])


if __name__ == "__main__":
    assert flat_list([1, 2, 3]) == [1, 2, 3], "Flat"
    assert flat_list([1, [2, 2, 2], 4]) == [1, 2, 2, 2, 4], "One"
    assert flat_list([[[2]], [4, [5, 6, [6], 6, 6, 6], 7]]) == [2, 4, 5, 6, 6, 6, 6, 6, 7], "Nested"
    assert flat_list([-1, [1, [-2], 1], -1]) == [-1, 1, -2, 1, -1], "In In"