Getting the exit code of a subprocess

[Jason]

Hello,

How can I find out the exit code of a process when using the subprocess module? I am passing an email message to a shell script and I need to know whether the shell script threw an error.

Here is my code:
p = Popen(cmd, stdout=None, stdin=PIPE, stderr=None)
p.communicate(input=msg)

I tried something like this:
e_stat = p.communicate(input=msg)

but the value of e_stat is always '(None, None)'


-- 
Thanks & best regards,
Jason Rissler