<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def save_config(config, logdir=None):
 """Save a new configuration by name. If a logging directory is specified, is will be created and the configuration will be stored there. Otherwise, a log message will be printed. Args: config: Configuration object. logdir: Location for writing summaries and checkpoints if specified. Returns: Configuration object. """

  if logdir:
    with config.unlocked:
      config.logdir = logdir
    message = 'Start a new run and write summaries and checkpoints to {}.'
    tf.logging.info(message.format(config.logdir))
    tf.gfile.MakeDirs(config.logdir)
    config_path = os.path.join(config.logdir, 'config.yaml')
    with tf.gfile.FastGFile(config_path, 'w') as file_:
      yaml.dump(config, file_, default_flow_style=False)
  else:
    message = (
        'Start a new run without storing summaries and checkpoints since no '
        'logging directory was specified.')
    tf.logging.info(message)
  return config