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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_default_by_index(self, index):
 """ Set the default dataset by its index. After changing the default dataset, all calls without explicitly specifying the dataset by index or alias will be redirected to this dataset. Args: index (int):
 The index of the dataset that should be made the default. Raises: DataInvalidIndex: If the index does not represent a valid dataset. """

        if index >= len(self._datasets):
            raise DataInvalidIndex('A dataset with index {} does not exist'.format(index))

        self._default_index = index