How to use the stevedore.exception function in stevedore

def _load_drivers(self):
        manager = stevedore.enabled.EnabledExtensionManager(
            namespace=self.MODULE_DRIVER_NAMESPACE,
            check_func=self._check_extension,
            invoke_on_load=True,
            invoke_kwds={})
        try:
            manager.map(self.add_driver_extension)
        except stevedore.exception.NoMatches:
            LOG.info("No module drivers loaded")

def load_driver(driver_name, *args):
    namespace = 'keystone.unified_limit.model'
    try:
        driver_manager = stevedore.DriverManager(namespace,
                                                 driver_name,
                                                 invoke_on_load=True,
                                                 invoke_args=args)
        return driver_manager.driver
    except stevedore.exception.NoMatches:
        msg = (_('Unable to find %(name)r driver in %(namespace)r.'))
        raise ImportError(msg % {'name': driver_name, 'namespace': namespace})

default_dispatcher = parsed_url.scheme
        if default_dispatcher == 'direct':
            LOG.warning('Direct publisher is deprecated for removal. Use '
                        'an explicit publisher instead, e.g. '
                        '"database", "file", ...')
            default_dispatcher = 'database'
        options = urlparse.parse_qs(parsed_url.query)
        self.dispatcher_name = options.get('dispatcher',
                                           [default_dispatcher])[-1]
        self._sample_dispatcher = None
        self._event_dispatcher = None

        try:
            self.sample_driver = driver.DriverManager(
                'ceilometer.dispatcher.meter', self.dispatcher_name).driver
        except stevedore.exception.NoMatches:
            self.sample_driver = None

        try:
            self.event_driver = driver.DriverManager(
                'ceilometer.dispatcher.event', self.dispatcher_name).driver
        except stevedore.exception.NoMatches:
            self.event_driver = None

def load_driver(namespace, driver_name, *args):
    try:
        driver_manager = stevedore.DriverManager(namespace,
                                                 driver_name,
                                                 invoke_on_load=True,
                                                 invoke_args=args)
        return driver_manager.driver
    except stevedore.exception.NoMatches:
        msg = (_('Unable to find %(name)r driver in %(namespace)r.'))
        raise ImportError(msg % {'name': driver_name, 'namespace': namespace})

def API(configuration=None):
    conf = configuration or cfg.CONF
    conf.register_opts(key_manager_opts, group='key_manager')

    try:
        mgr = driver.DriverManager("castellan.drivers",
                                   conf.key_manager.backend,
                                   invoke_on_load=True,
                                   invoke_args=[conf])
        return mgr.driver
    except exception.NoMatches:
        LOG.warning("Deprecation Warning : %s is not a stevedore based driver,"
                    " trying to load it as a class", conf.key_manager.backend)
        cls = importutils.import_class(conf.key_manager.backend)
        return cls(configuration=conf)

def device_manager(device_cfg):
    device_type = device_cfg.get('device_type', '')
    try:
        mgr = stevedore.driver.DriverManager(
            namespace=GENERIC_SWITCH_NAMESPACE,
            name=device_type,
            invoke_on_load=True,
            invoke_args=(device_cfg,),
            on_load_failure_callback=_load_failure_hook
        )
    except stevedore.exception.NoUniqueMatch as exc:
        raise gsw_exc.GenericSwitchEntrypointLoadError(
            ep='.'.join((GENERIC_SWITCH_NAMESPACE, device_type)),
            err=exc)
    return mgr.driver

options = urlparse.parse_qs(parsed_url.query)
        self.dispatcher_name = options.get('dispatcher',
                                           [default_dispatcher])[-1]
        self._sample_dispatcher = None
        self._event_dispatcher = None

        try:
            self.sample_driver = driver.DriverManager(
                'ceilometer.dispatcher.meter', self.dispatcher_name).driver
        except stevedore.exception.NoMatches:
            self.sample_driver = None

        try:
            self.event_driver = driver.DriverManager(
                'ceilometer.dispatcher.event', self.dispatcher_name).driver
        except stevedore.exception.NoMatches:
            self.event_driver = None