Add load specific answer from answer file using student name

Adds function `load_answer_from_student_name`,
`load_answer_from_loaded_file` to ExerciseRegistry API.
`load_answer_from_loaded_file` does what `load_answer` did before.
`load_answer` requires now an additional argument an `answers_filename`.
`load_answer_from_student_name` allows to load specific answers without
loading the entire file which can conflict with entries that do not have
yet a corresponding widget.

src/scwidgets/exercise/_widget_exercise_registry.py

@@ -101,7 +101,7 @@ def load(self) -> Union[str, Exception]:
             raise ValueError(
                 "No exercise key given on initialization, save cannot be used"
             )
-        return self._exercise_registry.load_answer(self._exercise_key)
+        return self._exercise_registry.load_answer_from_loaded_file(self._exercise_key)
 
     @property
     def exercise_registry(self):
@@ -341,26 +341,65 @@ def create_new_file_from_student_name(self, student_name: str):
 
             self._loaded_file_name = answers_filename
 
-    def load_answer(self, exercise_key: Hashable) -> str:
+    def load_answer_from_student_name(
+        self, student_name: str, exercise_key: Union[Hashable, ExerciseWidget]
+    ):
         """
-        Only works when file has been loaded
+        Loads the answer with key `exercise_key` from the file corresponding to
+        `student_name`.
 
-        :param exercise_key:
-            unique exercise key for widget to store, so it can be reloaded persistently
-            after a restart of the python kernel
+        :raises KeyError: Corresponding widget to exercise_key cannot be found
+        :raises KeyError: Corresponding key in file cannot be found
+        :raises FileNotFoundError: If the file cannot be found
+        :param student_name: The name of the student
+        :param exercise_key: Unique exercise key for widget to store, so it can
+            be reloaded persistently after a restart of the python kernel
+        """
+        self.load_answer(self.get_answer_filename(student_name), exercise_key)
+
+    def load_answer_from_loaded_file(
+        self, exercise_key: Union[Hashable, ExerciseWidget]
+    ) -> str:
+        """
+        Loads the answer with key `exercise_key` from the currently loaded file.
+
+        :raises ValueError: No have has been loaded
+        :raises KeyError: Corresponding widget to exercise_key cannot be found
+        :raises KeyError: Corresponding key in file cannot be found
+        :raises FileNotFoundError: If the file cannot be found
+        :param exercise_key: Unique exercise key for widget to store, so it can
+            be reloaded persistently after a restart of the python kernel
         """
+        if self._loaded_file_name is None:
+            raise ValueError("No file has been loaded.")
+
+        self.load_answer(self._loaded_file_name, exercise_key)
+        return f"Exercise has been loaded from file {self._loaded_file_name!r}."
+
+    def load_answer(
+        self, answers_filename: str, exercise_key: Union[Hashable, ExerciseWidget]
+    ):
+        """
+        Loads the answer with key `exercise_key` from the `answer_filename`.
+
+        :raises KeyError: Corresponding widget to exercise_key cannot be found
+        :raises KeyError: Corresponding key in file cannot be found
+        :raises FileNotFoundError: If the file cannot be found
+        :param answers_filename: The file with the answer
+        :param exercise_key: Unique exercise key for widget to store, so it can
+            be reloaded persistently after a restart of the python kernel
+        """
+        if isinstance(exercise_key, ExerciseWidget):
+            exercise_key = exercise_key.exercise_key
+
         if exercise_key not in self._widgets.keys():
             raise KeyError(
                 f"There is no widget registered with exercise key {exercise_key!r}."
             )
-        if self._loaded_file_name is None:
-            raise ValueError("No file has been selected in the dropdown list.")
-
-        answers_filename = self._loaded_file_name
 
         if not (os.path.exists(answers_filename)):
             raise FileNotFoundError(
-                "Selected file does not exist anymore. Maybe you have renamed "
+                f"The file {answers_filename!r} does not exist. Maybe you have renamed "
                 "or deleted it? Please choose another file or create a new one."
             )
 
@@ -375,9 +414,6 @@ def load_answer(self, exercise_key: Hashable) -> str:
         else:
             self._widgets[exercise_key].answer = answers[exercise_key]
         self._loaded_file_name = answers_filename
-        return f"Exercise has been loaded from file {answers_filename!r}."
-
-        self._answers_files_dropdown.value
 
     def load_file_from_dropdown(self) -> str:
         """
@@ -410,7 +446,7 @@ def load_file(self, answers_filename: str):
 
         if not (os.path.exists(answers_filename)):
             raise FileNotFoundError(
-                "Selected file does not exist anymore. Maybe you have renamed "
+                f"The file {answers_filename!r} does not exist. Maybe you have renamed "
                 "or deleted it? Please choose another file or create a new one."
             )
 

tests/test_answer.py

@@ -213,7 +213,8 @@ def test_load_file_from_dropdown(self):
         # Tests if error is raised on moved file
         os.rename(f"{self.prefix}-{self.student_name}.json", "tmp.json")
         with pytest.raises(
-            FileNotFoundError, match=r".*Selected file does not exist anymore.*"
+            FileNotFoundError,
+            match=r".*The file 'pytest-test-answer-registry.json' does not exist.*",
         ):
             answer_registry.load_file_from_dropdown()
         os.rename("tmp.json", f"{self.prefix}-{self.student_name}.json")
@@ -236,18 +237,26 @@ def test_load_file_from_dropdown(self):
         assert answer_widget_1.answer == "update_1"
         assert answer_widget_2.answer == "update_2"
 
-    def test_load_answer(self):
+    def test_load_answer_from_loaded_file(self):
         answers = {"exercise_1": "answer_1", "exercise_2": "answer_2"}
         with open(f"{self.prefix}-{self.student_name}.json", "w") as answer_file:
             json.dump(answers, answer_file)
 
         answer_registry = ExerciseRegistry(filename_prefix=self.prefix)
+        with pytest.raises(
+            ValueError,
+            match=r".*No file has been loaded*",
+        ):
+            answer_registry.load_answer_from_loaded_file("notkey")
 
+        # To avoid the no loaded file error
+        answer_registry._loaded_file_name = "some"
         with pytest.raises(
             KeyError,
             match=r".*There is no widget registered with exercise key 'notkey'.*",
         ):
-            answer_registry.load_answer("notkey")
+            answer_registry.load_answer_from_loaded_file("notkey")
+        answer_registry._loaded_file_name = None
 
         exercise_key_1 = "exercise_1"
         answer_widget_1 = mock_answer_widget(answer_registry, exercise_key_1)
@@ -259,10 +268,8 @@ def test_load_answer(self):
         answer_registry._answers_files_dropdown.value = (
             answer_registry._create_new_file_dropdown_option()
         )
-        with pytest.raises(
-            ValueError, match=r".*No file has been selected in the dropdown list.*"
-        ):
-            answer_registry.load_answer(exercise_key_1)
+        with pytest.raises(ValueError, match=r".*No file has been loaded.*"):
+            answer_registry.load_answer_from_loaded_file(exercise_key_1)
         # select back file to load
         answer_registry._answers_files_dropdown.value = (
             f"{self.prefix}-{self.student_name}.json"
@@ -272,15 +279,16 @@ def test_load_answer(self):
         # Tests if error is raised on moved file
         os.rename(f"{self.prefix}-{self.student_name}.json", "tmp.json")
         with pytest.raises(
-            FileNotFoundError, match=r".*Selected file does not exist anymore.*"
+            FileNotFoundError,
+            match=r".*The file 'pytest-test-answer-registry.json' does not exist.*",
         ):
-            answer_registry.load_answer(exercise_key_1)
+            answer_registry.load_answer_from_loaded_file(exercise_key_1)
         os.rename("tmp.json", f"{self.prefix}-{self.student_name}.json")
 
         # Test that file is contains only the updated answer
         answer_widget_1.answer = "update_1"
         answer_widget_2.answer = "update_2"
-        result = answer_registry.load_answer(exercise_key_1)
+        result = answer_registry.load_answer_from_loaded_file(exercise_key_1)
         assert (
             result == "Exercise has been loaded from file "
             "'pytest-test-answer-registry.json'."