Merge pull request 'update npu train.py' (#8) from liuzx into master

Reviewed-on: https://openi.pcl.ac.cn/OpenIOSSG/OpenI_Cloudbrain_Example/pulls/8

npu_mnist_example/train.py

@@ -68,7 +68,10 @@ if __name__ == "__main__":
     net_loss = nn.SoftmaxCrossEntropyWithLogits(sparse=True, reduction="mean")
     net_opt = nn.Momentum(network.trainable_params(), cfg.lr, cfg.momentum)
     time_cb = TimeMonitor(data_size=ds_train.get_dataset_size())
-    load_param_into_net(network, load_checkpoint(os.path.join(Mindspore_MNIST_Example_Model_path, "checkpoint_lenet-1_1875.ckpt")))
+    # load_param_into_net(network, load_checkpoint(os.path.join(Mindspore_MNIST_Example_Model_path, "checkpoint_lenet-1_1875.ckpt")))
+    if os.path.exists(os.path.join(Mindspore_MNIST_Example_Model_path, "checkpoint_lenet-1_1875.ckpt")):
+        load_param_into_net(network, load_checkpoint(os.path.join(Mindspore_MNIST_Example_Model_path, "checkpoint_lenet-1_1875.ckpt")))
+
     if args.device_target != "Ascend":
         model = Model(network,
                       net_loss,