code: def last_metric_eval(multiplexer, session_name, metric_name):
    
    try:
      run, tag = run_tag_from_session_and_metric(session_name, metric_name)
      tensor_events = multiplexer.Tensors(run=run, tag=tag)
    except KeyError as e:
      raise KeyError(
          'Can\'t find metric %s for session: %s. Underlying error message: %s'
          % (metric_name, session_name, e))
    last_event = tensor_events[-1]
    # TODO(erez): Raise HParamsError if the tensor is not a 0-D real scalar.
    return (last_event.wall_time,
            last_event.step,
            tf.make_ndarray(last_event.tensor_proto).item())
docs: Returns the last evaluations of the given metric at the given session.
  
    Args:
      multiplexer: The EventMultiplexer instance allowing access to
          the exported summary data.
      session_name: String. The session name for which to get the metric
          evaluations.
      metric_name: api_pb2.MetricName proto. The name of the metric to use.
  
    Returns:
      A 3-tuples, of the form [wall-time, step, value], denoting
      the last evaluation of the metric, where wall-time denotes the wall time
      in seconds since UNIX epoch of the time of the evaluation, step denotes
      the training step at which the model is evaluated, and value denotes the
      (scalar real) value of the metric.
  
    Raises:
      KeyError if the given session does not have the metric.