message: Include more relevant info in this `constant_value()` error message.
diff: @@ -708,7 +708,7 @@ def ShapeEquals(tensor_proto, shape):
  def _ConstantValue(tensor, partial):
  # TODO(touts): Support Variables?
  if not isinstance(tensor, ops.Tensor):
  - raise TypeError("tensor is not a Tensor")
  + raise TypeError("%r is not a Tensor, has type %s" % (tensor, type(tensor)))
  if tensor.op.type == "Const":
  return MakeNdarray(tensor.op.get_attr("value"))
  elif tensor.op.type == "Shape":
  