fixed up handling of empty return values

Author: tclose

pydra/compose/base/helpers.py

@@ -253,11 +253,10 @@ def extract_function_inputs_and_outputs(
             elif output is ty.Any:
                 output = return_type
             outputs = {output_name: output}
+    elif outputs == [] or return_type in (None, type(None)):
+        outputs = {}
     else:
-        if return_type not in (None, type(None)):
-            outputs = {"out": return_type}
-        else:
-            outputs = {}
+        outputs = {"out": return_type}
     return inputs, outputs
 
 

pydra/compose/python.py

@@ -239,6 +239,10 @@ def _run(self, job: "Job[PythonTask]", rerun: bool = True) -> None:
         return_names = [f.name for f in task_fields(self.Outputs)]
         if returned is None:
             job.return_values = {nm: None for nm in return_names}
+        elif not return_names:
+            raise ValueError(
+                f"No output fields were specified, but the function returned {returned}"
+            )
         elif len(return_names) == 1:
             # if only one element in the fields, everything should be returned together
             job.return_values[return_names[0]] = returned

pydra/compose/tests/test_python_fields.py

@@ -427,25 +427,25 @@ def TestFunc(a: A):
 
 
 def test_no_outputs1():
-    """Test function tasks with object inputs"""
+    """Test function tasks with no outputs specified by None return type"""
 
     @python.define
     def TestFunc(a: A) -> None:
         pass
 
     outputs = TestFunc(a=A(x=7))()
-    assert len(outputs) == 0
+    assert not task_fields(outputs)
 
 
 def test_no_outputs2():
-    """Test function tasks with object inputs"""
+    """Test function tasks with no outputs set explicitly"""
 
     @python.define(outputs=[])
     def TestFunc(a: A):
         pass
 
     outputs = TestFunc(a=A(x=7))()
-    assert len(outputs) == 0
+    assert not task_fields(outputs)
 
 
 def test_no_outputs_fail():
@@ -455,7 +455,5 @@ def test_no_outputs_fail():
     def TestFunc(a: A):
         return a
 
-    with pytest.raises(
-        ValueError, match="Returns an output but no outputs are defined"
-    ):
+    with pytest.raises(ValueError, match="No output fields were specified"):
         TestFunc(a=A(x=7))()