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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 set_npartitions(self, npartitions=None):
 """ Set the number of partitions to use for dask """

        if npartitions is None:
            self._npartitions = cpu_count() * 2
        else:
            self._npartitions = npartitions
        return self