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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 add_on_connection_close_callback(self):
 """ Add an on close callback that will be invoked by pika when RabbitMQ closes the connection to the publisher unexpectedly. """

        self._logger.debug('Adding connection close callback')
        self._connection.add_on_close_callback(self.on_connection_closed)