Fix 361 (#367)

* check if N==0, and handle this case

* change position of comment

* Address comments from shuhei

autoPyTorch/pipeline/components/training/trainer/__init__.py

@@ -293,6 +293,13 @@ def _fit(self, X: Dict[str, Any], y: Any = None, **kwargs: Any) -> 'TrainerChoic
                 writer=writer,
             )
 
+            # its fine if train_loss is None due to `is_max_time_reached()`
+            if train_loss is None:
+                if self.budget_tracker.is_max_time_reached():
+                    break
+                else:
+                    raise RuntimeError("Got an unexpected None in `train_loss`.")
+
             val_loss, val_metrics, test_loss, test_metrics = None, {}, None, {}
             if self.eval_valid_each_epoch(X):
                 val_loss, val_metrics = self.choice.evaluate(X['val_data_loader'], epoch, writer)
@@ -334,6 +341,9 @@ def _fit(self, X: Dict[str, Any], y: Any = None, **kwargs: Any) -> 'TrainerChoic
             if 'cuda' in X['device']:
                 torch.cuda.empty_cache()
 
+        if self.run_summary.is_empty():
+            raise RuntimeError("Budget exhausted without finishing an epoch.")
+
         # wrap up -- add score if not evaluating every epoch
         if not self.eval_valid_each_epoch(X):
             val_loss, val_metrics = self.choice.evaluate(X['val_data_loader'], epoch, writer)

autoPyTorch/pipeline/components/training/trainer/base_trainer.py

@@ -179,6 +179,16 @@ def repr_last_epoch(self) -> str:
         string += '=' * 40
         return string
 
+    def is_empty(self) -> bool:
+        """
+        Checks if the object is empty or not
+
+        Returns:
+            bool
+        """
+        # if train_loss is empty, we can be sure that RunSummary is empty.
+        return not bool(self.performance_tracker['train_loss'])
+
 
 class BaseTrainerComponent(autoPyTorchTrainingComponent):
 
@@ -277,7 +287,7 @@ def _scheduler_step(
 
     def train_epoch(self, train_loader: torch.utils.data.DataLoader, epoch: int,
                     writer: Optional[SummaryWriter],
-                    ) -> Tuple[float, Dict[str, float]]:
+                    ) -> Tuple[Optional[float], Dict[str, float]]:
         """
         Train the model for a single epoch.
 
@@ -317,6 +327,9 @@ def train_epoch(self, train_loader: torch.utils.data.DataLoader, epoch: int,
                     epoch * len(train_loader) + step,
                 )
 
+        if N == 0:
+            return None, {}
+
         self._scheduler_step(step_interval=StepIntervalUnit.epoch, loss=loss_sum / N)
 
         if self.metrics_during_training:

test/test_pipeline/components/training/test_training.py

@@ -236,6 +236,43 @@ def test_train_step(self):
             lr = optimizer.param_groups[0]['lr']
             assert lr == target_lr
 
+    def test_train_epoch_no_step(self):
+        """
+        This test checks if max runtime is reached
+        for an epoch before any train_step has been
+        completed. In this case we would like to
+        return None for train_loss and an empty
+        dictionary for the metrics.
+        """
+        device = torch.device('cpu')
+        model = torch.nn.Linear(1, 1).to(device)
+        optimizer = torch.optim.Adam(model.parameters(), lr=1)
+        data_loader = unittest.mock.MagicMock(spec=torch.utils.data.DataLoader)
+        ms = [3, 5, 6]
+        params = {
+            'metrics': [],
+            'device': device,
+            'task_type': constants.TABULAR_REGRESSION,
+            'labels': torch.Tensor([]),
+            'metrics_during_training': False,
+            'budget_tracker': BudgetTracker(budget_type='runtime', max_runtime=0),
+            'criterion': torch.nn.MSELoss,
+            'optimizer': optimizer,
+            'scheduler': torch.optim.lr_scheduler.MultiStepLR(optimizer, milestones=ms, gamma=2),
+            'model': model,
+            'step_interval': StepIntervalUnit.epoch
+        }
+        trainer = StandardTrainer()
+        trainer.prepare(**params)
+
+        loss, metrics = trainer.train_epoch(
+            train_loader=data_loader,
+            epoch=0,
+            writer=None
+        )
+        assert loss is None
+        assert metrics == {}
+
 
 class TestStandardTrainer(BaseTraining):
     def test_regression_epoch_training(self, n_samples):

test/test_pipeline/test_tabular_classification.py

@@ -1,6 +1,7 @@
 import os
 import re
 import unittest
+import unittest.mock
 
 from ConfigSpace.hyperparameters import (
     CategoricalHyperparameter,
@@ -491,3 +492,30 @@ def test_train_pipeline_with_runtime(fit_dictionary_tabular_dummy):
 
     # More than 200 epochs would have pass in 5 seconds for this dataset
     assert len(run_summary.performance_tracker['start_time']) > 100
+
+
+@pytest.mark.parametrize("fit_dictionary_tabular_dummy", ["classification"], indirect=True)
+def test_train_pipeline_with_runtime_max_reached(fit_dictionary_tabular_dummy):
+    """
+    This test makes sure that the pipeline raises an
+    error in case no epoch has finished successfully
+    due to max runtime reached
+    """
+
+    # Convert the training to runtime
+    fit_dictionary_tabular_dummy.pop('epochs', None)
+    fit_dictionary_tabular_dummy['budget_type'] = 'runtime'
+    fit_dictionary_tabular_dummy['runtime'] = 5
+    fit_dictionary_tabular_dummy['early_stopping'] = -1
+
+    pipeline = TabularClassificationPipeline(
+        dataset_properties=fit_dictionary_tabular_dummy['dataset_properties'])
+
+    cs = pipeline.get_hyperparameter_search_space()
+    config = cs.get_default_configuration()
+    pipeline.set_hyperparameters(config)
+
+    with unittest.mock.patch('autoPyTorch.pipeline.components.training.trainer.BudgetTracker') as patch:
+        patch.is_max_time_reached.return_value = True
+        with pytest.raises(RuntimeError):
+            pipeline.fit(fit_dictionary_tabular_dummy)