Change assert to exception raising.

train.py

@@ -81,9 +81,11 @@ parser.add_argument(
     help="Vocabulary filepath. (default: %(default)s)")
 parser.add_argument(
     "--init_model_path",
-    default='models/params.tar.gz',
+    default=None,
     type=str,
-    help="Model path for initialization. (default: %(default)s)")
+    help="If set None, the training will start from scratch. "
+    "Otherwise, the training will resume from "
+    "the existing model of this path. (default: %(default)s)")
 args = parser.parse_args()
 
 
@@ -124,7 +126,8 @@ def train():
     if args.init_model_path is None:
         parameters = paddle.parameters.create(cost)
     else:
-        assert os.path.isfile(args.init_model_path), "Invalid model."
+        if not os.path.isfile(args.init_model_path):
+            raise IOError("Invalid model!")
         parameters = paddle.parameters.Parameters.from_tar(
             gzip.open(args.init_model_path))
     optimizer = paddle.optimizer.Adam(