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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _init_topics(self):
 """Set up initial subscription of mysensors topics."""

        _LOGGER.info('Setting up initial MQTT topic subscription')
        init_topics = [
            '{}/+/+/0/+/+'.format(self._in_prefix),
            '{}/+/+/3/+/+'.format(self._in_prefix),
        ]
        self._handle_subscription(init_topics)
        if not self.persistence:
            return
        topics = [
            '{}/{}/{}/{}/+/+'.format(
                self._in_prefix, str(sensor.sensor_id), str(child.id),
                msg_type) for sensor in self.sensors.values()
            for child in sensor.children.values()
            for msg_type in (int(self.const.MessageType.set),
                             int(self.const.MessageType.req))
        ]
        topics.extend([
            '{}/{}/+/{}/+/+'.format(
                self._in_prefix, str(sensor.sensor_id),
                int(self.const.MessageType.stream))
            for sensor in self.sensors.values()])
        self._handle_subscription(topics)