How to use the mpf.core.utility_functions.Util.string_to_class function in mpf

self.doc_sections['config_players'] = dict()

        for name, module_ in self.mpfconfig['mpf']['config_players'].items():
            self.doc_sections['config_players'
                              ]['{}_player'.format(name)] = module_

        self.doc_sections['platforms'] = self.mpfconfig['mpf']['platforms']

        for plugin in Util.string_to_list(self.mpfconfig['mpf']['plugins']):
            name = plugin.split('.')[-2]
            self.doc_sections['machine'][name] = plugin

        self.doc_sections['devices'] = dict()

        for device in self.mpfconfig['mpf']['device_modules']:
            device_cls = Util.string_to_class(device)
            name = device_cls.collection
            self.doc_sections['devices'][name] = device

        self.doc_sections['modes'] = dict()

        for name in [x for x in
                     os.walk(os.path.join(os.pardir, 'mpf', 'modes'))][0][1]:

            if name.startswith('__'):
                continue

            class_name = ''.join([x.capitalize() for x in name.split('_')])

            self.doc_sections['modes'][name] = (
                'mpf.modes.{0}.code.{0}.{1}'.format(name, class_name))

def _load_scriptlets(self):
        if 'scriptlets' in self.config:
            self.config['scriptlets'] = self.config['scriptlets'].split(' ')

            self.log.debug("Loading scriptlets...")

            for scriptlet in self.config['scriptlets']:

                self.log.debug("Loading '%s' scriptlet", scriptlet)

                scriptlet_obj = Util.string_to_class(self.config['mpf']['paths']['scriptlets'] + "." + scriptlet)(
                    machine=self,
                    name=scriptlet.split('.')[1])

                self.scriptlets.append(scriptlet_obj)

def _load_scriptlets(self):
        if 'scriptlets' in self.config:
            self.config['scriptlets'] = self.config['scriptlets'].split(' ')

            self.log.debug("Loading scriptlets...")

            for scriptlet in self.config['scriptlets']:

                self.log.debug("Loading '%s' scriptlet", scriptlet)

                scriptlet_obj = Util.string_to_class(self.config['mpf']['paths']['scriptlets'] + "." + scriptlet)(
                    machine=self,
                    name=scriptlet.split('.')[1])

                self.scriptlets.append(scriptlet_obj)

def _load_scriptlets(self):
        if 'mc_scriptlets' in self.machine_config:
            self.machine_config['mc_scriptlets'] = (
                self.machine_config['mc_scriptlets'].split(' '))

            self.log.debug("Loading scriptlets...")

            for scriptlet in self.machine_config['mc_scriptlets']:

                self.log.debug("Loading '%s' scriptlet", scriptlet)

                scriptlet_obj = Util.string_to_class(
                    self.machine_config['mpf-mc']['paths']['scriptlets'] +
                    "." + scriptlet)(mc=self,
                                     name=scriptlet.split('.')[1])

                self.scriptlets.append(scriptlet_obj)

def _load_core_modules(self):
        self.log.debug("Loading core modules...")
        for name, module in self.config['mpf']['core_modules'].items():
            self.log.debug("Loading '%s' core module", module)
            m = Util.string_to_class(module)(self)
            setattr(self, name, m)

def _load_plugins(self):
        self.log.debug("Loading plugins...")

        # TODO: This should be cleaned up. Create a Plugins base class and
        # classmethods to determine if the plugins should be used.

        for plugin in Util.string_to_list(
                self.config['mpf']['plugins']):

            self.log.debug("Loading '%s' plugin", plugin)

            plugin_obj = Util.string_to_class(plugin)(self)
            self.plugins.append(plugin_obj)

def load_devices_config(self, validate=True):
        """Load all devices."""
        if validate:
            for device_type in self.machine.config['mpf']['device_modules']:

                device_cls = Util.string_to_class(device_type)

                collection_name, config_name = device_cls.get_config_info()

                if config_name not in self.machine.config:
                    continue

                # Get the config section for these devices
                collection = getattr(self.machine, collection_name)
                config = self.machine.config[config_name]
                if not config:
                    self.machine.config[config_name] = config = {}
                if not isinstance(config, dict):
                    self.raise_config_error("Format of collection {} is invalid.".format(collection_name), 1)

                # validate config
                for device_name in config: