fix import error in docs that use on the cloud

tutorials/source_zh_cn/advanced_use/use_on_the_cloud.md

@@ -89,7 +89,7 @@ ModelArts使用对象存储服务（Object Storage Service，简称OBS）进行
 1. 在ModelArts运行的脚本必须配置`data_url`和`train_url`，分别对应数据存储路径(OBS路径)和训练输出路径(OBS路径)。
 
     ``` python
-    import parser
+    import argparse
 
     parser = argparse.ArgumentParser(description='ResNet-50 train.')
     parser.add_argument('--data_url', required=True, default=None, help='Location of data.')
@@ -160,6 +160,8 @@ MindSpore暂时没有提供直接访问OBS数据的接口，需要通过MoXing
 
     ```python
     import os
+    from mindspore import context
+    from mindspore.train.model import ParallelMode
 
     device_num = int(os.getenv('RANK_SIZE'))
     if device_num > 1:
@@ -176,6 +178,7 @@ MindSpore暂时没有提供直接访问OBS数据的接口，需要通过MoXing
 
 ``` python
 import os
+import argparse
 from mindspore import context
 from mindspore.train.model import ParallelMode
 import mindspore.dataset.engine as de
@@ -194,8 +197,8 @@ def create_dataset(dataset_path):
 def resnet50_train(args_opt):
     if device_num > 1:
         context.set_auto_parallel_context(device_num=device_num,
-                                        parallel_mode=ParallelMode.DATA_PARALLEL,
-                                        mirror_mean=True)
+                                          parallel_mode=ParallelMode.DATA_PARALLEL,
+                                          mirror_mean=True)
     train_dataset = create_dataset(local_data_path)
 
 if __name__ == '__main__':
@@ -212,10 +215,12 @@ if __name__ == '__main__':
 
 ``` python
 import os
+import argparse
 from mindspore import context
 from mindspore.train.model import ParallelMode
 import mindspore.dataset.engine as de
 
+# adapt to cloud: used for downloading data
 import moxing as mox
 
 device_id = int(os.getenv('DEVICE_ID'))
@@ -230,19 +235,17 @@ def create_dataset(dataset_path):
     return ds
 
 def resnet50_train(args_opt):
-    epoch_size = args_opt.epoch_size
-    # define local data path
+    # adapt to cloud: define local data path
     local_data_path = '/cache/data'
 
-    context.set_context(mode=context.GRAPH_MODE)
     if device_num > 1:
         context.set_auto_parallel_context(device_num=device_num,
-                                        parallel_mode=ParallelMode.DATA_PARALLEL,
-                                        mirror_mean=True)
-        # define distributed local data path
+                                          parallel_mode=ParallelMode.DATA_PARALLEL,
+                                          mirror_mean=True)
+        # adapt to cloud: define distributed local data path
         local_data_path = os.path.join(local_data_path, str(device_id))
 
-    # data download
+    # adapt to cloud: download data from obs to local location
     print('Download data.')
     mox.file.copy_parallel(src_url=args_opt.data_url, dst_url=local_data_path)
 
@@ -250,7 +253,9 @@ def resnet50_train(args_opt):
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser(description='ResNet-50 train.')
+    # adapt to cloud: get obs data path
     parser.add_argument('--data_url', required=True, default=None, help='Location of data.')
+    # adapt to cloud: get obs output path
     parser.add_argument('--train_url', required=True, default=None, help='Location of training outputs.')
     parser.add_argument('--epoch_size', type=int, default=90, help='Train epoch size.')
     args_opt, unknown = parser.parse_known_args()