add functions to inspect model and optimizer status to trainer.py (#29838)

* add functions to get number of params which require grad, get optimizer group for parameters and get learning rates of param groups to trainer.py

* add tests and raise ValueError when optimizer is None

* add second layer to test and freeze its weigths

* check if torch is available before running tests

* use decorator to check if torch is available
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* fix test indentation
Co-authored-by: Zach Mueller <muellerzr@gmail.com>

---------
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>
Co-authored-by: Zach Mueller <muellerzr@gmail.com>

src/transformers/trainer.py

@@ -1049,6 +1049,36 @@ class Trainer:
 
         return self.optimizer
 
+    def get_num_trainable_parameters(self):
+        """
+        Get the number of trainable parameters.
+        """
+        return sum(p.numel() for p in self.model.parameters() if p.requires_grad)
+
+    def get_learning_rates(self):
+        """
+        Returns the learning rate of each parameter from self.optimizer.
+        """
+        if self.optimizer is None:
+            raise ValueError("Trainer optimizer is None, please make sure you have setup the optimizer before.")
+        return [group["lr"] for group in self.optimizer.param_groups]
+
+    def get_optimizer_group(self, param: Optional[Union[str, torch.nn.parameter.Parameter]] = None):
+        """
+        Returns optimizer group for a parameter if given, else returns all optimizer groups for params.
+
+        Args:
+            param (`str` or `torch.nn.parameter.Parameter`, *optional*):
+                The parameter for which optimizer group needs to be returned.
+        """
+        if self.optimizer is None:
+            raise ValueError("Trainer optimizer is None, please make sure you have setup the optimizer before.")
+        if param is not None:
+            for group in self.optimizer.param_groups:
+                if param in group["params"]:
+                    return group
+        return [group["params"] for group in self.optimizer.param_groups]
+
     @staticmethod
     def get_optimizer_cls_and_kwargs(
         args: TrainingArguments, model: Optional[PreTrainedModel] = None

tests/trainer/test_trainer.py

@@ -3832,3 +3832,41 @@ class HyperParameterSearchBackendsTest(unittest.TestCase):
             list(ALL_HYPERPARAMETER_SEARCH_BACKENDS.keys()),
             list(HPSearchBackend),
         )
+
+
+@require_torch
+class OptimizerAndModelInspectionTest(unittest.TestCase):
+    def test_get_num_trainable_parameters(self):
+        model = nn.Sequential(nn.Linear(128, 64), nn.Linear(64, 32))
+        # in_features * out_features + bias
+        layer_1 = 128 * 64 + 64
+        layer_2 = 64 * 32 + 32
+        trainer = Trainer(model=model)
+        self.assertEqual(trainer.get_num_trainable_parameters(), layer_1 + layer_2)
+        # Freeze the last layer
+        for param in model[-1].parameters():
+            param.requires_grad = False
+        self.assertEqual(trainer.get_num_trainable_parameters(), layer_1)
+
+    def test_get_learning_rates(self):
+        model = nn.Sequential(nn.Linear(128, 64))
+        trainer = Trainer(model=model)
+        with self.assertRaises(ValueError):
+            trainer.get_learning_rates()
+        trainer.create_optimizer()
+        self.assertEqual(trainer.get_learning_rates(), [5e-05, 5e-05])
+
+    def test_get_optimizer_group(self):
+        model = nn.Sequential(nn.Linear(128, 64))
+        trainer = Trainer(model=model)
+        # ValueError is raised if optimizer is None
+        with self.assertRaises(ValueError):
+            trainer.get_optimizer_group()
+        trainer.create_optimizer()
+        # Get groups
+        num_groups = len(trainer.get_optimizer_group())
+        self.assertEqual(num_groups, 2)
+        # Get group of parameter
+        param = next(model.parameters())
+        group = trainer.get_optimizer_group(param)
+        self.assertIn(param, group["params"])