execute pg_dump via python

I am using zope on windows with an external python method to backup my
database. I am struggling to run the following command:

pg_dump.exe database > file

I have tried using os.popen - no luck
and also subprocess.Popen.

eg:
import subprocess

subprocess.Popen(['c:/dir/dir/pg_dump.exe','database','>','c:/dir/dir/output
file'])

The command string works perfectly in a terminal. Does anyone know how I
should be doing this? I get no errors or traceback when I try the method
through Zope.

regards
garry