diff --git a/monai/handlers/classification_saver.py b/monai/handlers/classification_saver.py
index 4481ae0fec..7f96591503 100644
--- a/monai/handlers/classification_saver.py
+++ b/monai/handlers/classification_saver.py
@@ -98,7 +98,14 @@ def attach(self, engine: Engine) -> None:
         if not engine.has_event_handler(self._finalize, Events.EPOCH_COMPLETED):
             engine.add_event_handler(Events.EPOCH_COMPLETED, self._finalize)
 
-    def _started(self, engine: Engine) -> None:
+    def _started(self, _engine: Engine) -> None:
+        """
+        Initialize internal buffers.
+
+        Args:
+            _engine: Ignite Engine, unused argument.
+
+        """
         self._outputs = []
         self._filenames = []
 
@@ -120,12 +127,12 @@ def __call__(self, engine: Engine) -> None:
                 o = o.detach()
             self._outputs.append(o)
 
-    def _finalize(self, engine: Engine) -> None:
+    def _finalize(self, _engine: Engine) -> None:
         """
         All gather classification results from ranks and save to CSV file.
 
         Args:
-            engine: Ignite Engine, it can be a trainer, validator or evaluator.
+            _engine: Ignite Engine, unused argument.
         """
         ws = idist.get_world_size()
         if self.save_rank >= ws:
diff --git a/monai/handlers/metrics_saver.py b/monai/handlers/metrics_saver.py
index d6aa0c7b9f..d4acc4abdb 100644
--- a/monai/handlers/metrics_saver.py
+++ b/monai/handlers/metrics_saver.py
@@ -105,7 +105,14 @@ def attach(self, engine: Engine) -> None:
         engine.add_event_handler(Events.ITERATION_COMPLETED, self._get_filenames)
         engine.add_event_handler(Events.EPOCH_COMPLETED, self)
 
-    def _started(self, engine: Engine) -> None:
+    def _started(self, _engine: Engine) -> None:
+        """
+        Initialize internal buffers.
+
+        Args:
+            _engine: Ignite Engine, unused argument.
+
+        """
         self._filenames = []
 
     def _get_filenames(self, engine: Engine) -> None:
diff --git a/monai/handlers/stats_handler.py b/monai/handlers/stats_handler.py
index 9251453b50..c5b749e6a2 100644
--- a/monai/handlers/stats_handler.py
+++ b/monai/handlers/stats_handler.py
@@ -143,14 +143,14 @@ def iteration_completed(self, engine: Engine) -> None:
         else:
             self._default_iteration_print(engine)
 
-    def exception_raised(self, engine: Engine, e: Exception) -> None:
+    def exception_raised(self, _engine: Engine, e: Exception) -> None:
         """
         Handler for train or validation/evaluation exception raised Event.
         Print the exception information and traceback. This callback may be skipped because the logic
         with Ignite can only trigger the first attached handler for `EXCEPTION_RAISED` event.
 
         Args:
-            engine: Ignite Engine, it can be a trainer, validator or evaluator.
+            _engine: Ignite Engine, unused argument.
             e: the exception caught in Ignite during engine.run().
 
         """
diff --git a/monai/handlers/tensorboard_handlers.py b/monai/handlers/tensorboard_handlers.py
index 11b487ec99..70196c5fea 100644
--- a/monai/handlers/tensorboard_handlers.py
+++ b/monai/handlers/tensorboard_handlers.py
@@ -173,6 +173,21 @@ def iteration_completed(self, engine: Engine) -> None:
         else:
             self._default_iteration_writer(engine, self._writer)
 
+    def _write_scalar(self, _engine: Engine, writer: SummaryWriter, tag: str, value: Any, step: int) -> None:
+        """
+        Write scale value into TensorBoard.
+        Default to call `SummaryWriter.add_scalar()`.
+
+        Args:
+            _engine: Ignite Engine, unused argument.
+            writer: TensorBoard or TensorBoardX writer, passed or created in TensorBoardHandler.
+            tag: tag name in the TensorBoard.
+            value: value of the scalar data for current step.
+            step: index of current step.
+
+        """
+        writer.add_scalar(tag, value, step)
+
     def _default_epoch_writer(self, engine: Engine, writer: SummaryWriter) -> None:
         """
         Execute epoch level event write operation.
@@ -188,11 +203,11 @@ def _default_epoch_writer(self, engine: Engine, writer: SummaryWriter) -> None:
         summary_dict = engine.state.metrics
         for name, value in summary_dict.items():
             if is_scalar(value):
-                writer.add_scalar(name, value, current_epoch)
+                self._write_scalar(engine, writer, name, value, current_epoch)
 
         if self.state_attributes is not None:
             for attr in self.state_attributes:
-                writer.add_scalar(attr, getattr(engine.state, attr, None), current_epoch)
+                self._write_scalar(engine, writer, attr, getattr(engine.state, attr, None), current_epoch)
         writer.flush()
 
     def _default_iteration_writer(self, engine: Engine, writer: SummaryWriter) -> None:
@@ -221,12 +236,20 @@ def _default_iteration_writer(self, engine: Engine, writer: SummaryWriter) -> No
                         " {}:{}".format(name, type(value))
                     )
                     continue  # not plot multi dimensional output
-                writer.add_scalar(
-                    name, value.item() if isinstance(value, torch.Tensor) else value, engine.state.iteration
+                self._write_scalar(
+                    _engine=engine,
+                    writer=writer,
+                    tag=name,
+                    value=value.item() if isinstance(value, torch.Tensor) else value,
+                    step=engine.state.iteration,
                 )
         elif is_scalar(loss):  # not printing multi dimensional output
-            writer.add_scalar(
-                self.tag_name, loss.item() if isinstance(loss, torch.Tensor) else loss, engine.state.iteration
+            self._write_scalar(
+                _engine=engine,
+                writer=writer,
+                tag=self.tag_name,
+                value=loss.item() if isinstance(loss, torch.Tensor) else loss,
+                step=engine.state.iteration,
             )
         else:
             warnings.warn(