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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 combineByKey(self, createCombiner, mergeValue, mergeCombiners, numPartitions=None):
 """ Return a new DStream by applying combineByKey to each RDD. """

        if numPartitions is None:
            numPartitions = self._sc.defaultParallelism

        def func(rdd):
            return rdd.combineByKey(createCombiner, mergeValue, mergeCombiners, numPartitions)
        return self.transform(func)