Add on_optimizer_step to callback options (#31095)

* Modified test

* Added on_optimizer_step to callbacks

* Move callback after step is called

* Added on optimizer step callback

src/transformers/trainer.py

@@ -2306,6 +2306,8 @@ class Trainer:
 
                     self.optimizer.step()
 
+                    self.control = self.callback_handler.on_optimizer_step(args, self.state, self.control)
+
                     optimizer_was_run = not self.accelerator.optimizer_step_was_skipped
                     if optimizer_was_run:
                         # Delay optimizer scheduling until metrics are generated

src/transformers/trainer_callback.py

@@ -345,6 +345,12 @@ class TrainerCallback:
         """
         pass
 
+    def on_optimizer_step(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
+        """
+        Event called after the optimizer step but before gradients are zeroed out. Useful for monitoring gradients.
+        """
+        pass
+
     def on_substep_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl, **kwargs):
         """
         Event called at the end of an substep during gradient accumulation.
@@ -470,6 +476,9 @@ class CallbackHandler(TrainerCallback):
         control.should_save = False
         return self.call_event("on_step_begin", args, state, control)
 
+    def on_optimizer_step(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
+        return self.call_event("on_optimizer_step", args, state, control)
+
     def on_substep_end(self, args: TrainingArguments, state: TrainerState, control: TrainerControl):
         return self.call_event("on_substep_end", args, state, control)
 

tests/trainer/test_trainer_callback.py

@@ -78,6 +78,9 @@ class MyTestTrainerCallback(TrainerCallback):
     def on_step_begin(self, args, state, control, **kwargs):
         self.events.append("on_step_begin")
 
+    def on_optimizer_step(self, args, state, control, **kwargs):
+        self.events.append("on_optimizer_step")
+
     def on_step_end(self, args, state, control, **kwargs):
         self.events.append("on_step_end")
 
@@ -148,7 +151,7 @@ class TrainerCallbackTest(unittest.TestCase):
             expected_events.append("on_epoch_begin")
             for _ in range(train_dl_len):
                 step += 1
-                expected_events += ["on_step_begin", "on_step_end"]
+                expected_events += ["on_step_begin", "on_optimizer_step", "on_step_end"]
                 if step % trainer.args.logging_steps == 0:
                     expected_events.append("on_log")
                 if trainer.args.eval_strategy == IntervalStrategy.STEPS and step % trainer.args.eval_steps == 0: