code: def set(file_name, key, value, new):
      
      db = XonoticDB.load_path(file_name)
      if key not in db and not new:
          click.echo('Key %s is not found in the database' % key, file=sys.stderr)
          sys.exit(1)
      else:
          db[key] = value
          db.save(file_name)
docs: Set a new value for the specified key.