BUG #14583: plpythonu : subprocess not working in function

The following bug has been logged on the website:

Bug reference: 14583
Logged by: Paulo B
Email address: paulo(dot)nuno(dot)leite(at)gmail(dot)com
PostgreSQL version: 9.5.6
Operating system: Windows
Description:

I have the following function that runs a command:

CREATE OR REPLACE FUNCTION public.classify_test()
RETURNS void AS
$BODY$
import os
from subprocess import Popen, PIPE
import subprocess
import os
from subprocess import Popen, PIPE

echo=Popen(('echo', '123'), shell=True)

p = subprocess.Popen(['python.exe', '-u','test.py'], stdin = echo.stdout,
universal_newlines = True, shell = True)

$BODY$
LANGUAGE plpythonu VOLATILE
COST 100;
ALTER FUNCTION public.classify_test()
OWNER TO postgres;

if I run this fuction as select classify_test() it will not run the python
script. However, if I run it in the command line it will work. It works as
well in SublimeText2 IDE. I have been trying to find what the bug or problem
is, but had no success. I am using python2.7, I have psycopg2 installed.

Why doesn't postgresql execute the python script?