Performance issue in the definition of test, Project/NeuralMachineTranslation/model/test.py(P1)

[DLPerf]

Hello, I found a performance issue in the definition of test, Project/NeuralMachineTranslation/model/test.py, tf.expand_dims(input=[1],axis=0) will be called repeatedly during program execution, resulting in reduced efficiency. I think it should be created before the loop.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.