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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, partitionFunc=portable_hash):
 """ Merge the values for each key using an associative and commutative reduce function. This will also perform the merging locally on each mapper before sending results to a reducer, similarly to a "combiner" in MapReduce. Output will be partitioned with C{numPartitions} partitions, or the default parallelism level if C{numPartitions} is not specified. Default partitioner is hash-partition. [('a', 2), ('b', 1)] """

        return self.combineByKey(lambda x: x, func, func, numPartitions, partitionFunc)