Fixed batch referenced before assignment

composer/trainer/trainer.py

@@ -3644,6 +3644,12 @@ def _iter_dataloader(self, trainer_mode: TrainerMode):
         # 0 = not finished, 1 = finished (using integer tensors so we can use dist.all_reduce)
         iter_finished = torch.zeros(1, dtype=torch.uint8)
         iter_finished = self.state.device.tensor_to_device(iter_finished)
+
+        # Initialize batch to avoid "referenced before assignment" warnings
+        # Unique sentinel value to differentiate uninitialized state and dataloader yielding None
+        sentinel = object()
+        batch = sentinel
+
         while True:
             try:
                 # [BEFORE/AFTER]_DATALOADER only runs while training
@@ -3668,6 +3674,10 @@ def _iter_dataloader(self, trainer_mode: TrainerMode):
             if iter_finished.item() == 1:
                 break
 
+            if batch is sentinel:
+                raise RuntimeError(
+                    "Batch should have been assigned or loop should have been broken. This shouldn't happen!",
+                )
             yield batch
 
     def _use_closures(self) -> bool: