How to use the mqttwarn.util.load_function function in mqttwarn

def test_load_function():

    # Load valid functions file
    py_mod = load_functions(filepath=funcfile)
    assert py_mod is not None

    # Load valid function
    func = load_function(name='foobar', py_mod=py_mod)
    assert func is not None

    # Load invalid function, function name does not exist in "funcfile"
    with pytest.raises(AttributeError) as excinfo:
        load_function(name='unknown', py_mod=py_mod)
    assert re.match("Function 'unknown' does not exist in '{}c?'".format(funcfile), str(excinfo.value))

def test_load_function():

    # Load valid functions file
    py_mod = load_functions(filepath=funcfile)
    assert py_mod is not None

    # Load valid function
    func = load_function(name='foobar', py_mod=py_mod)
    assert func is not None

    # Load invalid function, function name does not exist in "funcfile"
    with pytest.raises(AttributeError) as excinfo:
        load_function(name='unknown', py_mod=py_mod)
    assert re.match("Function 'unknown' does not exist in '{}c?'".format(funcfile), str(excinfo.value))

def datamap(self, name, topic):
        """
        Invoke function "name" loaded from the "functions" Python module.

        :param name:    Function name to invoke
        :param topic:   Topic to pass to the invoked function
        :return:        Return value of function invocation
        """

        val = None
        try:
            func = load_function(name=name, py_mod=self.config.functions)
            try:
                val = func(topic, self.srv)  # new version
            except TypeError:
                val = func(topic)       # legacy
        except:
            raise

        return val

def filter(self, name, topic, payload, section=None):
        """
        Invoke function "name" loaded from the "functions" Python module.
        Return that function's True/False.

        :param name:    Function name to invoke
        :param topic:   Topic to pass to the invoked function
        :param payload: Payload to pass to the invoked function
        :return:        Return value of function invocation
        """

        rc = False
        try:
            func = load_function(name=name, py_mod=self.config.functions)
            try:
                rc = func(topic, payload, section, self.srv)  # new version
            except TypeError:
                rc = func(topic, payload)                     # legacy signature
        except:
            raise

        return rc

def topic_target_list(self, name, topic, data):
        """
        Invoke function "name" loaded from the "functions" Python module.
        Computes dynamic topic subscription targets.
        Obtains MQTT topic and transformation data.

        :param name:    Function name to invoke
        :param topic:   Topic to pass to the invoked function
        :param data:    Data to pass to the invoked function
        :return:        Return value of function invocation
        """

        val = None
        try:
            func = load_function(name=name, py_mod=self.config.functions)
            val = func(topic=topic, data=data, srv=self.srv)
        except:
            raise

        return val

# Launch worker threads to operate on queue
    logger.info('Starting %s worker threads' % cf.num_workers)
    for i in range(cf.num_workers):
        t = threading.Thread(target=processor, kwargs={'worker_id': i})
        t.daemon = True
        t.start()

    # If the config file has a [cron] section, the key names therein are
    # functions from 'myfuncs.py' which should be invoked periodically.
    # The key's value (must be numeric!) is the period in seconds.

    if cf.has_section('cron'):
        for name, val in cf.items('cron'):
            try:
                func = load_function(name=name, py_mod=cf.functions)
                cron_options = parse_cron_options(val)
                interval = cron_options['interval']
                logger.debug('Scheduling function "{name}" as periodic task ' \
                              'to run each {interval} seconds via [cron] section'.format(name=name, interval=interval))
                service = make_service(mqttc=mqttc, name='mqttwarn.cron')
                ptlist[name] = PeriodicThread(callback=func, period=interval, name=name, srv=service, now=asbool(cron_options.get('now')))
                ptlist[name].start()
            except AttributeError:
                logger.error("[cron] section has function [%s] specified, but that's not defined" % name)
                continue

def alldata(self, name, topic, data):
        """
        Invoke function "name" loaded from the "functions" Python module.

        :param name:    Function name to invoke
        :param topic:   Topic to pass to the invoked function
        :param data:    Data to pass to the invoked function
        :return:        Return value of function invocation
        """

        val = None
        try:
            func = load_function(name=name, py_mod=self.config.functions)
            val = func(topic, data, self.srv)
        except:
            raise

        return val