And subprocess is available in 2.6, too. It looks like a well-designed API and certainly makes it easy to run external filters on data. For example, to get the output of 'tidy -q' on a string s:

  proc = subprocess.Popen(['tidy', '-q'], stdin=PIPE, stdout=PIPE, stderr=PIPE)
  (tidyout, tidyerr) = proc.communicate(input=s)
  if proc.returncode != 0:
      ...