new_contents: from homework_parser.file_parser import detect_plugin
  
  from sys import argv, stdin, stdout, stderr, exit
  
  if __name__ == "__main__":
      in_format = argv[1]
      out_format = argv[2]
      out_plugin = detect_plugin(out_format)
  
      if out_plugin is None:
          print >> stderr, ('out-plugin %s not found' % out_format)
          exit(-1)
  
      in_plugin = detect_plugin(in_format)
      if in_plugin is None:
          print >> stderr, ('in-plugin %s not found' % in_format)
          exit(-1)
       
      if len(argv) == 4:
          with open(argv[3]) as f:
              data = in_plugin.read_from_file(f)
      else:
          data = in_plugin.read_from_file(stdin)
      
      out_plugin.write_to_file(stdout, data)
  
subject: add __main__ file