The SAVEPOINT example presents a subtransaction instead of using PostgreSQL SAVEPOINT.  See https://www.postgresql.org/docs/current/sql-savepoint.html

Interesting article.  However, the SAVEPOINT example is misleading, presenting a subtransaction, kind of nested transaction of PostgreSQL.  Does psycopg2 support SAVEPOINTs of PostgresSQL, see https://www.postgresql.org/docs/current/sql-savepoint.html

This is an important topic, but the author unfortunately presents NULL as a 3-value logic value in both tables instead of UNKOWN. Joe Celko has presented this precisely in...