How to use the cfgrib.messages function in cfgrib

def test_build_data_var_components_no_encode():
    index = messages.FileStream(path=TEST_DATA).index(dataset.ALL_KEYS).subindex(paramId=130)
    dims, data_var, coord_vars = dataset.build_variable_components(index=index)
    assert dims == {'number': 10, 'dataDate': 2, 'dataTime': 2, 'level': 2, 'values': 7320}
    assert data_var.data.shape == (10, 2, 2, 2, 7320)

    # equivalent to not np.isnan without importing numpy
    assert data_var.data[:, :, :, :, :].mean() > 0.0

def test_FileIndex_errors():
    class MyMessage(messages.ComputedKeysMessage):
        computed_keys = {'error_key': lambda m: 1 / 0}

    stream = messages.FileStream(TEST_DATA, message_class=MyMessage)
    res = messages.FileIndex.from_filestream(stream, ['paramId', 'error_key'])
    assert res['paramId'] == [129, 130]
    assert len(res) == 2
    assert list(res) == ['paramId', 'error_key']
    assert res['error_key'] == ['undef']

return dims, data


COMPUTED_KEYS = {
    'time': (from_grib_date_time, to_grib_date_time),
    'step': (from_grib_step, to_grib_step),
    'valid_time': (
        functools.partial(from_grib_date_time, date_key='validityDate', time_key='validityTime'),
        functools.partial(to_grib_date_time, date_key='validityDate', time_key='validityTime'),
    ),
    'verifying_time': (from_grib_month, None),
}


@attr.attrs()
class CfMessage(messages.ComputedKeysMessage):
    computed_keys = attr.attrib(default=COMPUTED_KEYS)

def build_dataset_attributes(index, filter_by_keys, encoding):
    attributes = enforce_unique_attributes(index, GLOBAL_ATTRIBUTES_KEYS, filter_by_keys)
    attributes['Conventions'] = 'CF-1.7'
    if 'GRIB_centreDescription' in attributes:
        attributes['institution'] = attributes['GRIB_centreDescription']
    attributes_namespace = {
        'cfgrib_version': __version__,
        'cfgrib_open_kwargs': json.dumps(encoding),
        'eccodes_version': messages.eccodes_version,
        'timestamp': datetime.datetime.now().isoformat().partition('.')[0],
    }
    history_in = (
        '{timestamp} GRIB to CDM+CF via '
        'cfgrib-{cfgrib_version}/ecCodes-{eccodes_version} with {cfgrib_open_kwargs}'
    )
    attributes['history'] = history_in.format(**attributes_namespace)
    return attributes