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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 start(self):
 """ Starts sending periodic HeartBeat operations. """

        def _heartbeat():
            if not self._client.lifecycle.is_live:
                return
            self._heartbeat()
            self._heartbeat_timer = self._client.reactor.add_timer(self._heartbeat_interval, _heartbeat)

        self._heartbeat_timer = self._client.reactor.add_timer(self._heartbeat_interval, _heartbeat)