bug fix

python/paddle/fluid/trainer.py

@@ -356,10 +356,14 @@ class Trainer(object):
             self._train_by_any_executor(event_handler, exe, num_epochs, reader)
 
     def _train_by_any_executor(self, event_handler, exe, num_epochs, reader):
-        epochs = [
-            epoch_id for epoch_id in range(num_epochs)
-            if epoch_id >= self.checkpoint.epoch_id
-        ]
+        if self.checkpoint:
+            epochs = [
+                epoch_id for epoch_id in range(num_epochs)
+                if epoch_id >= self.checkpoint.epoch_id
+            ]
+        else:
+            epochs = [epoch_id for epoch_id in range(num_epochs)]
+
         for epoch_id in epochs:
             event_handler(BeginEpochEvent(epoch_id))
             for step_id, data in enumerate(reader()):