def primary_from_id(self, tax_id):
        """
        Returns primary taxonomic name associated with tax_id
        """
        s = select([self.names.c.tax_name],
                   and_(self.names.c.tax_id == tax_id,
                        self.names.c.is_primary))
        res = s.execute()
        output = res.fetchone()

        if not output:
            msg = 'value "{}" not found in names.tax_id'.format(tax_id)
            raise ValueError(msg)
        else:
            return output[0]
Returns primary taxonomic name associated with tax_id