How to use the awe.chart.DictLevelsTransformer.from_str function in awe

def test_dict_level_transformer():
    def generate_data(v1, v2):
        level3 = lambda: {'l3_key1': v1, 'l3_key2': v2}
        level2 = lambda: {'l2_key1': level3(), 'l2_key2': level3(), 'l2_key3': level3()}
        level1 = lambda: {'l1_key1': level2(), 'l1_key2': level2()}
        return level1()

    transformer = chart.DictLevelsTransformer.from_str('13to2')
    assert transformer.key == '13to2'

    assert transformer.transform(None) == {}
    assert transformer.transform([]) == {}

    transform = transformer.transform([generate_data(1, 2), generate_data(3, 4)])
    for k, v in transform.items():
        transform[k]['series'] = sorted(transform[k]['series'], key=lambda s: s['name'])

    assert transform == {
        'l1_key1 l3_key1': {
            'series': [{'data': [(0, 1), (0, 3)], 'name': 'l2_key1'},
                       {'data': [(0, 1), (0, 3)], 'name': 'l2_key2'},
                       {'data': [(0, 1), (0, 3)], 'name': 'l2_key3'}],
            'title': 'l1_key1 l3_key1',
            'type': 'line'

def test_dict_level_transformer_timed_tuples():
    ts = 1000.12
    expected_ts = int(ts * 1000)
    transformer = chart.DictLevelsTransformer.from_str('1to2')
    for ds in [list, tuple]:
        transform = transformer.transform([ds((ts, {'c': {'d': 1234}}))])
        assert transform == {
            'c': {'series': [{'data': [(expected_ts, 1234)], 'name': 'd'}], 'title': 'c', 'type': 'line'}
        }

def _get_transformer(transform):
        transformer = transform or 'noop'
        if isinstance(transformer, Transformer):
            return transformer
        elif isinstance(transformer, dict):
            transformer_key = transformer.pop('type')
            return transformer_classes[transformer_key](**transformer)
        if isinstance(transformer, six.string_types):
            if transformer in transformers:
                return transformers[transformer]
            maybe_dict_transformer = DictLevelsTransformer.from_str(transformer)
            if maybe_dict_transformer:
                transformers[maybe_dict_transformer.key] = maybe_dict_transformer
                return maybe_dict_transformer
        raise ValueError('No matching transformer found for {}'.format(transform))