Handle-none-outputs

docs/source/tutorial/2-advanced-execution.ipynb

@@ -351,8 +351,8 @@
     "how to utilise containers and add support for other software environments.\n",
     "\n",
     "It is also possible to specify functions to run at hooks that are immediately before and after\n",
-    "the task is executed by passing a `pydra.engine.spec.TaskHooks` object to the `hooks`\n",
-    "keyword arg. The callable should take the `pydra.engine.core.Job` object as its only\n",
+    "the task is executed by passing a `pydra.engine.hooks.TaskHooks` object to the `hooks`\n",
+    "keyword arg. The callable should take the `pydra.engine.job.Job` object as its only\n",
     "argument and return None. The available hooks to attach functions are:\n",
     "\n",
     "* pre_run: before the task cache directory is created\n",
@@ -415,7 +415,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "wf12",
+   "display_name": "wf13",
    "language": "python",
    "name": "python3"
   },
@@ -429,7 +429,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.5"
+   "version": "3.13.1"
   }
  },
  "nbformat": 4,

docs/source/tutorial/7-canonical-form.ipynb

@@ -34,8 +34,8 @@
     "Default values can also be set directly, as with Attrs classes.\n",
     "\n",
     "In order to allow static type-checkers to check the type of outputs of tasks added\n",
-    "to workflows, it is also necessary to explicitly extend from the `pydra.engine.python.Task`\n",
-    "and `pydra.engine.python.Outputs` classes (they are otherwise set as bases by the\n",
+    "to workflows, it is also necessary to explicitly extend from the `pydra.compose.python.Task`\n",
+    "and `pydra.compose.python.Outputs` classes (they are otherwise set as bases by the\n",
     "`define` method implicitly). Thus the \"canonical form\" of Python task is as\n",
     "follows"
    ]

pydra/compose/base/helpers.py

@@ -183,7 +183,7 @@
         input_types[p.name] = type_hints.get(p.name, ty.Any)
         if p.default is not inspect.Parameter.empty:
             input_defaults[p.name] = p.default
-    if inputs:
+    if inputs is not None:
         if not isinstance(inputs, dict):
             raise ValueError(
                 f"Input names ({inputs}) should not be provided when "
@@ -218,41 +218,43 @@
                 f"value {default}"
             )
     return_type = type_hints.get("return", ty.Any)
-    if outputs and len(outputs) > 1:
-        if return_type is not ty.Any:
-            if ty.get_origin(return_type) is not tuple:
-                raise ValueError(
-                    f"Multiple outputs specified ({outputs}) but non-tuple "
-                    f"return value {return_type}"
-                )
-            return_types = ty.get_args(return_type)
-            if len(return_types) != len(outputs):
-                raise ValueError(
-                    f"Length of the outputs ({outputs}) does not match that "
-                    f"of the return types ({return_types})"
-                )
-            output_types = dict(zip(outputs, return_types))
-        else:
-            output_types = {o: ty.Any for o in outputs}
-        if isinstance(outputs, dict):
-            for output_name, output in outputs.items():
-                if isinstance(output, Out) and output.type is ty.Any:
-                    output.type = output_types[output_name]
+    if outputs:
+        if len(outputs) > 1:
+            if return_type is not ty.Any:
+                if ty.get_origin(return_type) is not tuple:
+                    raise ValueError(
+                        f"Multiple outputs specified ({outputs}) but non-tuple "
+                        f"return value {return_type}"
+                    )
+                return_types = ty.get_args(return_type)
+                if len(return_types) != len(outputs):
+                    raise ValueError(
+                        f"Length of the outputs ({outputs}) does not match that "
+                        f"of the return types ({return_types})"
+                    )
+                output_types = dict(zip(outputs, return_types))
+            else:
+                output_types = {o: ty.Any for o in outputs}
+            if isinstance(outputs, dict):
+                for output_name, output in outputs.items():
+                    if isinstance(output, Out) and output.type is ty.Any:
+                        output.type = output_types[output_name]
+            else:
+                outputs = output_types
         else:
-            outputs = output_types
-
-    elif outputs:
-        if isinstance(outputs, dict):
-            output_name, output = next(iter(outputs.items()))
-        elif isinstance(outputs, list):
-            output_name = outputs[0]
-            output = ty.Any
-        if isinstance(output, Out):
-            if output.type is ty.Any:
-                output.type = return_type
-        elif output is ty.Any:
-            output = return_type
-        outputs = {output_name: output}
+            if isinstance(outputs, dict):
+                output_name, output = next(iter(outputs.items()))
+            elif isinstance(outputs, list):
+                output_name = outputs[0]
+                output = ty.Any
+            if isinstance(output, Out):
+                if output.type is ty.Any:
+                    output.type = return_type
+            elif output is ty.Any:
+                output = return_type
+            outputs = {output_name: output}
+    elif outputs == [] or return_type in (None, type(None)):
+        outputs = {}
     else:
         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

@@ -424,3 +424,54 @@
 
     outputs = TestFunc(a=A(x=7))()
     assert outputs.out == 7
+
+
+def test_no_outputs1():
+    """Test function tasks with no outputs specified by None return type"""
+
+    @python.define
+    def TestFunc1(a: A) -> None:
+        print(a)
+
+    outputs = TestFunc1(a=A(x=7))()
+    assert not task_fields(outputs)
+
+
+def test_no_outputs2():
+    """Test function tasks with no outputs set explicitly"""
+
+    @python.define(outputs=[])
+    def TestFunc2(a: A):
+        print(a)
+
+    outputs = TestFunc2(a=A(x=7))()
+    assert not task_fields(outputs)
+
+
+def test_no_outputs_fail():
+    """Test function tasks with object inputs"""
+
+    @python.define(outputs=[])
+    def TestFunc3(a: A):
+        return a
+
+    with pytest.raises(ValueError, match="No output fields were specified"):
+        TestFunc3(a=A(x=7))()
+
+
+def test_only_one_output_fail():
+
+    with pytest.raises(ValueError, match="Multiple outputs specified"):
+
+        @python.define(outputs=["out1", "out2"])
+        def TestFunc4(a: A) -> A:
+            return a
+
+
+def test_incorrect_num_outputs_fail():
+
+    with pytest.raises(ValueError, match="Length of the outputs"):
+
+        @python.define(outputs=["out1", "out2"])
+        def TestFunc5(a: A) -> tuple[A, A, A]:
+            return a, a, a

pyproject.toml

@@ -140,7 +140,7 @@ testpaths = ["pydra"]
 log_cli_level = "INFO"
 xfail_strict = true
 addopts = [
-  "-svx",
+  "-svv",
   "-ra",
   "--strict-config",
   "--strict-markers",