def METHOD_NAME():
    data = {
        "hash": {
            "dict": {"array": [1, 2, [1, 2, {"#": 123}]]},
            "list": [1, 2, [1, 2, {"mapping": 123}]],
        },
        "list": [1, 2, [1, 2, {"mapping": 123}]],
    }
    expected = {
        "hash-dict-array-0": 1,
        "hash-dict-array-1": 2,
        "hash-dict-array-2-0": 1,
        "hash-dict-array-2-1": 2,
        "hash-dict-array-2-2-#": 123,
        "hash-list-0": 1,
        "hash-list-1": 2,
        "hash-list-2-0": 1,
        "hash-list-2-1": 2,
        "hash-list-2-2-mapping": 123,
        "list-0": 1,
        "list-1": 2,
        "list-2-0": 1,
        "list-2-1": 2,
        "list-2-2-mapping": 123,
    }
    assert py3.flatten_dict(data, delimiter="-") == expected
    returned = py3.flatten_dict(data, delimiter="-")
    print("returned data")
    print(pformat(returned))
    assert returned == expected