(Python) reproduce psycopg2 TransactionRollbackError on ISOLATION_LEVEL_SERIALIZABLE mode

reproduce_psycopg2.py

# -*- coding: utf-8 -*-

import psycopg2
from datetime import datetime


# ISOLATION_LEVEL_AUTOCOMMIT
# ISOLATION_LEVEL_READ_COMMITTED
# ISOLATION_LEVEL_REPEATABLE_READ
# ISOLATION_LEVEL_SERIALIZABLE
def reproduce_psycopg2():
    """
    psycopg2.extensions.TransactionRollbackError: could not serialize access due to read/write dependencies among transactions
    DETAIL:  Reason code: Canceled on identification as a pivot, during commit attempt.
    HINT:  The transaction might succeed if retried.
    """

    conn1 = psycopg2.connect("dbname=h2 user=h2 password=h2 host=localhost")
    conn1.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE)
    cur1 = conn1.cursor()

    conn2 = psycopg2.connect("dbname=h2 user=h2 password=h2 host=localhost")
    conn2.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE)
    cur2 = conn2.cursor()

    cur1.execute("SELECT * FROM antz WHERE id IN (1);")
    cur2.execute("SELECT * FROM antz WHERE id IN (2);")
    cur1.execute("UPDATE antz SET fired_at = '%s' WHERE id = 1;" % datetime.now())
    cur2.execute("UPDATE antz SET fired_at = '%s' WHERE id = 2;" % datetime.now())
    conn1.commit()
    conn2.commit()


# begin;
# set transaction isolation level serializable; -- T1
# select * from antz where id in (1,2); -- T1
# update antz set task = 'welcome' where id = 1; -- T1
# commit; -- T1

# begin;
# set transaction isolation level serializable; -- T2
# select * from antz where id in (1,2); -- T2
# update antz set task = 'welcome' where id = 2; -- T2
# commit; -- T2. Prints out error

if __name__ == '__main__':
    reproduce_psycopg2()