code: def evaluate_model(self,
                       accuracy,
                       num_steps,
                       feed_vars=(),
                       feed_data=None,
                       summary_tag=None,
                       print_every=0):
      
      if not hasattr(self, '_saver'):
        raise ValueError('Before evaluating, you must initialize the model with '
                         'load_from_checkpoint, prepare or saver.')
      self._run_init_test_vars_op()
      if (not isinstance(accuracy, collections.Sequence) or
          isinstance(accuracy, six.string_types)):
        accuracy = (accuracy,)
        if summary_tag:
          summary_tag = (summary_tag,)
      if summary_tag and len(summary_tag) != len(accuracy):
        raise ValueError(
            'If summaries are requested, there must be a tag per accuracy node.')
  
      result = self.run_model(accuracy,
                              num_steps,
                              feed_vars=feed_vars,
                              feed_data=feed_data,
                              print_every=print_every,
                              allow_initialize=False)
      assert len(result) == len(accuracy) + 1, (
          'results is wrong length, was %s but should be 1 longer than %s' %
          (result, accuracy))
      if summary_tag:
        self.add_summaries(result[0], *zip(summary_tag, result[1:]))
      return result[1:]
docs: Evaluates the given model.
  
      Args:
        accuracy: The metric that is being evaluated or a tuple of metrics.
        num_steps: The number of steps to run in the evaluator.
        feed_vars: A list or tuple of the variables that will be fed.
        feed_data: A generator that produces tuples of the same length as
          feed_vars.
        summary_tag: If provided, the final result of running the model will be
          published to this tag.
        print_every: Print a summary every so many steps, use 0 to disable.
      Returns:
        The accuracy.
      Raises:
        ValueError: If the wrong number of summary tags are provided or previously
          running QueueRunners haven't been stopped.