Fixes issue #1868 regarding TypeError: ZipperIterDataPipe instance doesn't have a valid length (#1954)

Co-authored-by: Svetlana Karslioglu <[email protected]>

Author: otioss

beginner_source/translation_transformer.py

@@ -309,7 +309,7 @@ def train_epoch(model, optimizer):
         optimizer.step()
         losses += loss.item()
 
-    return losses / len(train_dataloader)
+    return losses / len(list(train_dataloader))
 
 
 def evaluate(model):
@@ -333,7 +333,7 @@ def evaluate(model):
         loss = loss_fn(logits.reshape(-1, logits.shape[-1]), tgt_out.reshape(-1))
         losses += loss.item()
 
-    return losses / len(val_dataloader)
+    return losses / len(list(val_dataloader))
 
 ######################################################################
 # Now we have all the ingredients to train our model. Let's do it!