[Fix] Check return type of FunctionalLoss

ppsci/loss/func.py

@@ -19,6 +19,8 @@
 from typing import Optional
 from typing import Union
 
+import paddle
+
 from ppsci.loss import base
 
 
@@ -34,7 +36,7 @@ class FunctionalLoss(base.Loss):
     $$
 
     Args:
-        loss_expr (Callable): expression of loss calculation.
+        loss_expr (Callable[..., paddle.Tensor]): Function for custom loss computation.
         weight (Optional[Union[float, Dict[str, float]]]): Weight for loss. Defaults to None.
 
     Examples:
@@ -63,11 +65,21 @@ class FunctionalLoss(base.Loss):
 
     def __init__(
         self,
-        loss_expr: Callable,
+        loss_expr: Callable[..., paddle.Tensor],
         weight: Optional[Union[float, Dict[str, float]]] = None,
     ):
         super().__init__(None, weight)
         self.loss_expr = loss_expr
 
-    def forward(self, output_dict, label_dict=None, weight_dict=None):
-        return self.loss_expr(output_dict, label_dict, weight_dict)
+    def forward(self, output_dict, label_dict=None, weight_dict=None) -> paddle.Tensor:
+        loss = self.loss_expr(output_dict, label_dict, weight_dict)
+
+        assert isinstance(
+            loss, (paddle.Tensor, paddle.static.Variable, paddle.pir.Value)
+        ), (
+            "Loss computed by custom function should be type of 'paddle.Tensor', "
+            f"'paddle.static.Variable' or 'paddle.pir.Value', but got {type(loss)}."
+            " Please check the return type of custom loss function."
+        )
+
+        return loss

test/loss/func.py

@@ -0,0 +1,30 @@
+import paddle
+import pytest
+
+from ppsci import loss
+
+__all__ = []
+
+
+def test_non_tensor_return_type():
+    """Test for biharmonic equation."""
+
+    def loss_func_return_tensor(input_dict, label_dict, weight_dict):
+        return (0.5 * (input_dict["x"] - label_dict["x"]) ** 2).sum()
+
+    def loss_func_reuturn_builtin_float(input_dict, label_dict, weight_dict):
+        return (0.5 * (input_dict["x"] - label_dict["x"]) ** 2).sum().item()
+
+    wrapped_loss1 = loss.FunctionalLoss(loss_func_return_tensor)
+    wrapped_loss2 = loss.FunctionalLoss(loss_func_reuturn_builtin_float)
+
+    input_dict = {"x": paddle.randn([10, 1])}
+    label_dict = {"x": paddle.zeros([10, 1])}
+
+    wrapped_loss1(input_dict, label_dict)
+    with pytest.raises(AssertionError):
+        wrapped_loss2(input_dict, label_dict)
+
+
+if __name__ == "__main__":
+    pytest.main()