BUG #14730: Passing an array of composites to a plpythonu function results in a list of strs

The following bug has been logged on the website:

Bug reference: 14730
Logged by: Peter Sutton
Email address: foxxy(at)foxdogstudios(dot)com
PostgreSQL version: 9.6.3
Operating system: Linux
Description:

Passing an array of composites to a plpythonu function results in a list of
strs, not a list of dicts or tuples as I expected. Here's an example:

BEGIN;

CREATE TABLE mytable (
col1 INTEGER
, col2 BOOLEAN
, col3 TEXT
);

INSERT INTO mytable VALUES
(1, TRUE , 'Text')
, (2, NULL , 'Text')
, (3, FALSE, NULL )
;

CREATE FUNCTION myfunc (ts mytable[]) RETURNS VOID
LANGUAGE plpythonu
AS $plpythonu$

from pprint import pformat
plpy.notice(pformat(ts))
if ts:
plpy.notice(type(ts[0]))

$plpythonu$;

SELECT myfunc(array_agg(t)) FROM mytable AS t;

-- psql:local/script.pgsql:28: NOTICE: ['(1,t,Text)', '(2,,Text)',
'(3,f,)']
-- psql:local/script.pgsql:28: NOTICE: <type 'str'>
-- myfunc
-- --------
--
-- (1 row)

SELECT myfunc(ARRAY[t]) FROM mytable AS t;

-- psql:local/script.pgsql:29: NOTICE: ['(1,t,Text)']
-- psql:local/script.pgsql:29: NOTICE: <type 'str'>
-- psql:local/script.pgsql:29: NOTICE: ['(2,,Text)']
-- psql:local/script.pgsql:29: NOTICE: <type 'str'>
-- psql:local/script.pgsql:29: NOTICE: ['(3,f,)']
-- psql:local/script.pgsql:29: NOTICE: <type 'str'>
-- myfunc
-- --------
--
--
--
-- (3 rows)

ROLLBACK;

https://gist.github.com/dj-foxxy/16ba42d0a76da2bf384353cc024682b0

I expected the items of list list to be tuple or dicts, e.g., [(1, True,
'Text'), ...].

Thanks, Peter.