Help replacing os.system call with subprocess call

[David Pratt]

Hi. I am trying to replace a system call with a subprocess call. I have 
tried subprocess.Popen and subprocess.call with but have not been 
successful. The command line would be:

svnadmin dump /my/repository > svndump.db

This is what I am using currently:

os.system('svnadmin dump %s > %s' % (svn_dir,
     os.path.join(backup_dir, 'svndump.db')))

Many thanks.