Add save topology for chapter 3

03.image_classification/train.py

@@ -79,6 +79,12 @@ def main():
     # Create trainer
     trainer = paddle.trainer.SGD(
         cost=cost, parameters=parameters, update_equation=momentum_optimizer)
+    
+    # Save the inference topology to protobuf.
+    inference_topology = paddle.topology.Topology(layers=out)
+    with open("inference_topology.pkl", 'wb') as f:
+        inference_topology.serialize_for_inference(f)
+
     trainer.train(
         reader=paddle.batch(
             paddle.reader.shuffle(