def _get_lineage(self, tax_id, merge_obsolete=True):
        """Return a list of [(rank, tax_id)] describing the lineage of
        tax_id. If ``merge_obsolete`` is True and ``tax_id`` has been
        replaced, use the corresponding value in table merged.

        """

        # Be sure we aren't working with an obsolete tax_id
        if merge_obsolete:
            tax_id = self._get_merged(tax_id)

        # Note: joining with ranks seems like a no-op, but for some
        # reason it results in a faster query using sqlite, as well as
        # an ordering from leaf --> root. Might be a better idea to
        # sort explicitly if this is the expected behavior, but it
        # seems like for the most part, the lineage is converted to a
        # dict and the order is irrelevant.
        cmd = """
        WITH RECURSIVE a AS (
         SELECT tax_id, parent_id, rank
          FROM {nodes}
          WHERE tax_id = {}
        UNION ALL
         SELECT p.tax_id, p.parent_id, p.rank
          FROM a JOIN {nodes} p ON a.parent_id = p.tax_id
        )
        SELECT a.rank, a.tax_id FROM a
        JOIN {ranks} using(rank)
        """.format(self.placeholder, nodes=self.nodes, ranks=self.ranks_table)

        # with some versions of sqlite3, an error is raised when no
        # rows are returned; with others, an empty list is returned.
        try:
            with self.engine.connect() as con:
                result = con.execute(cmd, (tax_id,))
                # reorder so that root is first
                lineage = result.fetchall()[::-1]
        except sqlalchemy.exc.ResourceClosedError:
            lineage = []

        if not lineage:
            raise ValueError('tax id "{}" not found'.format(tax_id))

        return lineage
Return a list of [(rank, tax_id)] describing the lineage of
        tax_id. If ``merge_obsolete`` is True and ``tax_id`` has been
        replaced, use the corresponding value in table merged.