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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 subscriber_count(self, destination=None):
 """ Returns a count of the number of subscribers. If destination is specified then it only returns count of subscribers for that specific destination. @param destination: The optional topic/queue destination (e.g. '/queue/foo') @type destination: C{str} """

        if destination:
            return len(self._queues[destination])
        else:
            # total them up
            total = 0
            for k in self._queues.keys():
                total += len(self._queues[k])
            return total