[Torchvision API] Exception for isolated objective operator execution

dali/python/nvidia/dali/experimental/torchvision/v2/compose.py

@@ -77,7 +77,7 @@ def _pipeline_function(op_list: Sequence, layout: str = "HWC", input_device: str
     """
     input_node = fn.external_source(name="input_data", layout=layout, device=input_device)
     for op in op_list:
-        input_node = op(input_node)
+        input_node = op._invoke(input_node)
     return input_node
 
 

dali/python/nvidia/dali/experimental/torchvision/v2/operator.py

@@ -242,7 +242,19 @@ def _kernel(self, data_input):
         pass
 
     def __call__(self, data_input):
+        """
+        Torchvision creates callable objects, but DALI Torchvision needs to implement a pipeline.
+        The pipeline is implemented in Compose class and uses _invoke to execute operators' logic.
+        """
+        raise RuntimeError(
+            f"Operator {self!r} is not directly callable. Use it only inside Compose pipeline."
+        )
 
+    def _invoke(self, data_input):
+        """
+        Private method is used to execute operator from a Compose pipeline
+        Note: Do not call directly
+        """
         type(self).verify_data(data_input)
 
         # Original input is transfered to GPU, before being preprocess_data.

dali/test/python/torchvision/test_tv_compose.py

@@ -422,3 +422,12 @@ def test_compose_non_uint8_dtype_resize(dtype):
     else:
         with assert_raises(RuntimeError):
             _ = dali_pipeline(test_tensor)
+
+
+def test_error_in_isolated_operators():
+    """Operators must not be called outside of Compose"""
+
+    test_tensor = torch.ones(5, 3, 10, 10, dtype=torch.uint8)
+    dali_resize = Resize(size=(7, 7))
+    with assert_raises(RuntimeError, glob="*is not directly callable*"):
+        _ = dali_resize(test_tensor)