def scalar_pb(tag, data, description=None):
  """Create a scalar summary_pb2.Summary protobuf.

  Arguments:
    tag: String tag for the summary.
    data: A 0-dimensional `np.array` or a compatible python number type.
    description: Optional long-form description for this summary, as a
      `str`. Markdown is supported. Defaults to empty.

  Raises:
    ValueError: If the type or shape of the data is unsupported.

  Returns:
    A `summary_pb2.Summary` protobuf object.
  """
  arr = np.array(data)
  if arr.shape != ():
    raise ValueError('Expected scalar shape for tensor, got shape: %s.'
                     % arr.shape)
  if arr.dtype.kind not in ('b', 'i', 'u', 'f'):  # bool, int, uint, float
    raise ValueError('Cast %s to float is not supported' % arr.dtype.name)
  tensor_proto = tensor_util.make_tensor_proto(arr.astype(np.float32))
  summary_metadata = metadata.create_summary_metadata(
      display_name=None, description=description)
  summary = summary_pb2.Summary()
  summary.value.add(tag=tag,
                    metadata=summary_metadata,
                    tensor=tensor_proto)
  return summary