I found the solution here: ps2pdf Docs
This works, here called from Python:
import subprocess
cmd=['gs', '-q', '-dSAFER', '-dNOPAUSE', '-dBATCH',
'-dDisableFAPI',
'-sOutputFile=%s' % pdf,
'-sDEVICE=pdfwrite',
'-c', '.setpdfwrite', '-f'
]
cmd.extend(ps_files)
subprocess.check_call(cmd)