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

        if alias not in self._aliases:
            raise DataInvalidAlias('A dataset with alias {} does not exist'.format(alias))

        self._default_index = self._aliases[alias]