postgresql - Python subprocess hangs with psql command -

i running following piece of python code (runs command in shell , grabs output or reports error)

import sys import subprocess def check_output(args, communicate=none, quiet=false, **kwargs):     stream in ["stdout", "stderr"]:         kwargs.setdefault(stream, subprocess.pipe)      proc = subprocess.popen(args, **kwargs)     try:         out, err = proc.communicate()     finally:         f in (proc.stdout, proc.stderr):             if f not none:                 f.close()         proc.wait()      if kwargs["stderr"] != subprocess.pipe:         err = ""      if proc.returncode != 0:         raise exception(args, proc.returncode, err)     else:         if not quiet:             sys.stderr.write(err)             sys.stderr.flush()     return out 

with following arguments:

env = dict(         pghost='{pg_host}',         pgport='{pg_port}',         pgdatabase='{pg_dbname}',         pguser='{pg_user}',         pgpassword='{pg_password}',       )  cmd = ['psql', '-c', "insert {ft_geom} select * {ft_geom_in};"].format(**tables) check_output(cmd, shell=true, env=env) 

here env contains pg[host|user|database|port|..] environment variables , tables contains names of 2 tables. when run code, hangs indefinitely on proc = subprocess.popen call. using python 2.6.5 on ubuntu 10.04.3 lts

i check no tables locked following:

select a.datname,          c.relname,          l.transactionid,          l.mode,          l.granted,          a.usename,          a.current_query,           a.query_start,          age(now(), a.query_start) "age",           a.procpid       pg_stat_activity      join pg_locks         l on l.pid = a.procpid      join pg_class         c on c.oid = l.relation     order a.query_start; 

and shows locks granted. not sure else at. need shell=true because commands more complex, requiring bash pipes. know should ideally pass stdout.pipe of 1 command other, not possible change @ moment.

running same command bash directly works expected, also, running without shell=true works

the problem didn't filter newline characters in tokens passed check_output, shell hang waiting more input. make sure escape tokens when pass them shell.