Where is the missing postgres-plpython-12 for Ubuntu 20.04, required for psycopg2? - postgresql

Question

There is no available package for postgres-plpython-12
https://packages.ubuntu.com/search?keywords=postgresql-plpython
The psycopg2 library does not work with plpython3 (or does it)?
psycopg2.errors.UndefinedFile: could not access file "$libdir/plpython2": No such file or directory
So how does anyone get psycopg2 working on Ubuntu >= 20.04 ?
The libpq* libraries are installed.
libpq-dev is already the newest version (13.4-1.pgdg18.04+1).
libpq5 is already the newest version (13.4-1.pgdg18.04+1).
Maybe everything must be on postgres-13? Since there seems to be no explicit candidates for libpq* version 12.x
The error above is generated by pytest-postgresql from
postgresql = <connection object at 0x7fa79feaf548; dsn: 'user=postgres password=xxx dbname=app_test host=127.0.0.1 port=15988 options=''', closed: 0>
#pytest.fixture
def postgresql_config(postgresql) -> Dict:
# https://github.com/ClearcodeHQ/pytest-postgresql#how-to-use
# https://github.com/ClearcodeHQ/pytest-postgresql#configuration
# see pytest.ini for configuration options
# assert isinstance(postgresql, connection)
dsn = postgresql.get_dsn_parameters()
passwd_data = Path(dsn["passfile"]).read_text().strip()
passwd = passwd_data.split(":")[-1]
dsn_path = f"{dsn['user']}:{passwd}#{dsn['host']}:{dsn['port']}"
db_url = f"postgresql+psycopg2://{dsn_path}/{dsn['dbname']}"
admin_config = {
"timeout": 10,
"host": dsn["host"],
"port": dsn["port"],
"dbname": dsn["dbname"],
"username": dsn["user"],
"password": passwd,
"url": db_url,
}
# - init the test-db using the postgres admin user
# - for some tips on idempotent DDL, see:
# https://www.depesz.com/2008/06/18/conditional-ddl/
cursor = postgresql.cursor()
for statement in sqlparse.split(_setup_sql):
if statement:
> cursor.execute(statement)
E psycopg2.errors.UndefinedFile: could not access file "$libdir/plpython2": No such file or directory