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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 reduceByKey(self, func, numPartitions=None):
 """ Return a new DStream by applying reduceByKey to each RDD. """

        if numPartitions is None:
            numPartitions = self._sc.defaultParallelism
        return self.combineByKey(lambda x: x, func, func, numPartitions)