code: def get_by_alias(self, alias):
          
          if alias not in self._aliases:
              raise DataInvalidAlias('A dataset with alias {} does not exist'.format(alias))
  
          return self.get_by_index(self._aliases[alias])
docs: Return a dataset by its alias.
  
          Args:
              alias (str): The alias of the dataset that should be returned.
  
          Raises:
              DataInvalidAlias: If the alias does not represent a valid dataset.