CREATE EXTENSION ltree_plpython3u CASCADE;
NOTICE:  installing required extension "plpython3u"
CREATE FUNCTION test1(val ltree) RETURNS int
LANGUAGE plpython3u
TRANSFORM FOR TYPE ltree
AS $$
plpy.info(repr(val))
return len(val)
$$;
SELECT test1('aa.bb.cc'::ltree);
INFO:  ['aa', 'bb', 'cc']
 test1 
-------
     3
(1 row)

CREATE FUNCTION test1n(val ltree) RETURNS int
LANGUAGE plpython3u
TRANSFORM FOR TYPE ltree
AS $$
plpy.info(repr(val))
return len(val)
$$;
SELECT test1n('aa.bb.cc'::ltree);
INFO:  ['aa', 'bb', 'cc']
 test1n 
--------
      3
(1 row)

CREATE FUNCTION test2() RETURNS ltree
LANGUAGE plpython3u
TRANSFORM FOR TYPE ltree
AS $$
return ['foo', 'bar', 'baz']
$$;
-- plpython to ltree is not yet implemented, so this will fail,
-- because it will try to parse the Python list as an ltree input
-- string.
SELECT test2();
ERROR:  ltree syntax error at character 1
CONTEXT:  while creating return value
PL/Python function "test2"