update error_string when target is out of bound (#40001)

python/paddle/nn/functional/loss.py

@@ -1667,11 +1667,11 @@ def cross_entropy(input,
             label_min = paddle.min(valid_label)
             label_max = paddle.max(valid_label)
             if label_min < 0:
-                raise ValueError("label should not out of bound, but got{}".
-                                 format(label_min))
+                raise ValueError("Target {} is out of lower bound.".format(
+                    label_min.item()))
             if label_max >= input.shape[axis]:
-                raise ValueError("label should not out of bound, but got{}".
-                                 format(label_max))
+                raise ValueError("Target {} is out of upper bound.".format(
+                    label_max.item()))
         if core.is_compiled_with_npu() or core.is_compiled_with_mlu():
             _, _, out = _C_ops.softmax_with_cross_entropy(
                 input, label, 'soft_label', soft_label, 'ignore_index',