Support update_func without arguments in CodeExercise

src/scwidgets/exercise/_widget_code_exercise.py

@@ -2,6 +2,7 @@
 # see https://stackoverflow.com/a/33533514
 from __future__ import annotations
 
+import inspect
 import types
 from platform import python_version
 from typing import Any, Callable, Dict, List, Optional, Union
@@ -67,7 +68,10 @@ def __init__(
         update_mode: str = "release",
         cue_outputs: Union[None, CueOutput, List[CueOutput]] = None,
         update_func: Optional[
-            Callable[[CodeExercise], Union[Any, Check.FunOutParamsT]]
+            Union[
+                Callable[[CodeExercise], Union[Any, Check.FunOutParamsT]],
+                Callable[[], Union[Any, Check.FunOutParamsT]],
+            ]
         ] = None,
         exercise_description: Optional[str] = None,
         exercise_title: Optional[str] = None,
@@ -82,7 +86,30 @@ def __init__(
             )
         self._update_mode = update_mode
 
-        self._update_func = update_func
+        self._update_func: Optional[
+            Union[
+                Callable[[CodeExercise], Union[Any, Check.FunOutParamsT]],
+                Callable[[], Union[Any, Check.FunOutParamsT]],
+            ]
+        ] = update_func
+
+        self._update_func_nb_nondefault_args: Optional[int]
+        if update_func is not None:
+            self._update_func_nb_nondefault_args = len(
+                [
+                    value
+                    for value in inspect.signature(update_func).parameters.values()
+                    if not isinstance(value.default, inspect._empty)
+                ]
+            )
+            if self._update_func_nb_nondefault_args > 1:
+                raise ValueError(
+                    f"The given update_func has "
+                    f"{self._update_func_nb_nondefault_args} parameters without "
+                    "defaults, but only zero or one are supported."
+                )
+        else:
+            self._update_func_nb_nondefault_args = None
 
         self._exercise_description = exercise_description
         if exercise_description is None:
@@ -639,7 +666,7 @@ def cue_outputs(self):
 
     def _on_click_update_action(self) -> bool:
         self._output.clear_output(wait=True)
-        raised_error = False
+        self._raised_error = False
         # runs code and displays output
         with self._output:
             try:
@@ -648,7 +675,10 @@ def _on_click_update_action(self) -> bool:
                         cue_output.clear_display(wait=True)
 
                 if self._update_func is not None:
-                    self._update_func(self)
+                    if self._update_func_nb_nondefault_args == 0:
+                        self._update_func()  # type: ignore[call-arg]
+                    else:
+                        self._update_func(self)  # type: ignore[call-arg]
                 elif self._code is not None:
                     self.run_code(**self.parameters)
 
@@ -657,18 +687,18 @@ def _on_click_update_action(self) -> bool:
                         cue_output.draw_display()
 
             except CodeValidationError as e:
-                raised_error = True
+                self._raised_error = True
                 raise e
             except Exception as e:
-                raised_error = True
+                self._raised_error = True
                 raise e
 
             # The clear_output command at the beginning of the function waits till
             # something is printed. If nothing is printed, it is not cleared. We
             # enforce it to be invoked by printing an empty string
             print("", end="")
 
-        return not (raised_error)
+        return not (self._raised_error)
 
     def run_update(self):
         """

tests/test_code.py

@@ -16,6 +16,10 @@
 
 class TestCodeInput:
     # fmt: off
+    @staticmethod
+    def mock_function_0():
+        return 0
+
     @staticmethod
     def mock_function_1(x, y):
         """
@@ -81,6 +85,7 @@ def get_code_exercise(
     include_checks=True,
     include_params=True,
     tunable_params=False,
+    update_func_argless=False,
     update_mode="manual",
 ):
     # Important:
@@ -109,9 +114,17 @@ def get_code_exercise(
     else:
         parameters = None
 
-    def update_print(code_ex: CodeExercise):
-        output = code_ex.run_code(**code_ex.parameters)
-        code_ex.cue_outputs[0].display_object = f"Output:\n{output}"
+    if update_func_argless:
+
+        def update_print():
+            output = code_ex.run_code(**code_ex.parameters)
+            code_ex.cue_outputs[0].display_object = f"Output:\n{output}"
+
+    else:
+
+        def update_print(code_ex: CodeExercise):
+            output = code_ex.run_code(**code_ex.parameters)
+            code_ex.cue_outputs[0].display_object = f"Output:\n{output}"
 
     code_ex = CodeExercise(
         code=code_input,
@@ -198,7 +211,7 @@ def test_compute_and_set_references(self, code_ex):
         "code_ex",
         [
             get_code_exercise(
-                [single_param_check(use_fingerprint=False, failing=False, buggy=False)]
+                [single_param_check(use_fingerprint=False, failing=False, buggy=False)],
             ),
             get_code_exercise(
                 [multi_param_check(use_fingerprint=False, failing=False)]
@@ -260,3 +273,52 @@ def print_success(code_ex: CodeExercise | None):
         exercise_registry.create_new_file()
         code_ex._save_button.click()
         os.remove("test_save_registry-student_name.json")
+
+    @pytest.mark.parametrize(
+        "code_ex",
+        [
+            get_code_exercise(
+                [],
+                code=TestCodeInput.mock_function_0,
+                update_func_argless=False,
+            ),
+            get_code_exercise(
+                [],
+                code=TestCodeInput.mock_function_0,
+                update_func_argless=True,
+            ),
+        ],
+    )
+    def test_run_update(self, code_ex):
+        """Test run_update"""
+        import io
+        from contextlib import redirect_stdout
+
+        buffer = io.StringIO()
+        code_ex._output = redirect_stdout(buffer)
+
+        def mock_clear_output(wait):
+            pass
+
+        code_ex._output.clear_output = mock_clear_output
+
+        # Be aware that the raised error is captured in the code_ex._output
+        # To debug failures in the test you have to manually run it in debug
+        # mode and execute `code_ex._update_button.click()` Redirecting stderr
+        # does des not workc
+        code_ex.run_update()
+        assert "Output:\n0" in buffer.getvalue()
+
+    def test_invalid_update_func(self):
+        """Test run_update for wrong input"""
+
+        def failing_update(a, b):
+            pass
+
+        with pytest.raises(
+            ValueError, match=r".*The given update_func has 2 parameters .*"
+        ):
+            CodeExercise(
+                code=TestCodeInput.mock_function_0,
+                update_func=failing_update,
+            )