code: def main(argv=None):
      
      if not argv:
          argv = sys.argv[1:]
  
      parser = argparse.ArgumentParser(description=_HELP_TEXT)
      parser.add_argument('input', nargs='?', default=None)
      parser.add_argument('output', nargs='?', default=None)
      parser.add_argument('--version', action='version',
                          version='%(prog)s ' + get_version())
      args = parser.parse_args(argv)
  
      if not args.input:
          print("No file specified", file=sys.stderr)
          sys.exit(1)
  
      try:
          with open(args.input, 'r') as f:
              res = mangle(f.read())
              if not args.output:
                  print(res, end='')
              else:
                  with open(args.output, 'w') as o:
                      o.write(res)
      except Exception as ex:
          print("Error mangling {}: {!s}".format(args.input, ex),
                file=sys.stderr)
          sys.exit(1)
docs: Command line entry point