def run_tag_from_session_and_metric(session_name, metric_name):
  """Returns a (run,tag) tuple storing the evaluations of the specified metric.

  Args:
    session_name: str.
    metric_name: MetricName protobuffer.
  Returns: (run, tag) tuple.
  """
  assert isinstance(session_name, six.string_types)
  assert isinstance(metric_name, api_pb2.MetricName)
  # os.path.join() will append a final slash if the group is empty; it seems
  # like multiplexer.Tensors won't recognize paths that end with a '/' so
  # we normalize the result of os.path.join() to remove the final '/' in that
  # case.
  run = os.path.normpath(os.path.join(session_name, metric_name.group))
  tag = metric_name.tag
  return run, tag