create extension if not exists plpython3u;

drop table if exists testpk, testfk;

create table testpk (id int primary key);

create table testfk(f1 int references testpk deferrable initially deferred);

DO
LANGUAGE plpython3u
$$
  plpy.execute("INSERT INTO testfk VALUES (0)")
  try:
    plpy.commit()
  except Exception as e:
    plpy.info('sqlstate: %s' % (e.sqlstate))
  plpy.info('after exception')
  plpy.execute("INSERT INTO testpk VALUES (1)")
  plpy.execute("INSERT INTO testfk VALUES (1)")
$$;

table testfk;