enhance error message, fix device bug

examples/image_classification/main.py

@@ -76,6 +76,9 @@ def main():
     device = set_device(FLAGS.device)
     fluid.enable_dygraph(device) if FLAGS.dynamic else None
 
+    model_list = [x for x in models.__dict__["__all__"]]
+    assert FLAGS.arch in model_list, "Expected FLAGS.arch in {}, but received {}".format(
+        model_list, FLAGS.arch)
     model = models.__dict__[FLAGS.arch](pretrained=FLAGS.eval_only and
                                         not FLAGS.resume)
 
@@ -94,7 +97,13 @@ def main():
             len(train_dataset) * 1. / FLAGS.batch_size / ParallelEnv().nranks),
         parameter_list=model.parameters())
 
-    model.prepare(optim, CrossEntropy(), Accuracy(topk=(1, 5)), inputs, labels)
+    model.prepare(
+        optim,
+        CrossEntropy(),
+        Accuracy(topk=(1, 5)),
+        inputs,
+        labels,
+        FLAGS.device)
 
     if FLAGS.eval_only:
         model.evaluate(
@@ -152,7 +161,7 @@ if __name__ == '__main__':
         type=str,
         help="checkpoint path to resume")
     parser.add_argument(
-        "--eval-only", action='store_true', help="enable dygraph mode")
+        "--eval-only", action='store_true', help="only evaluate the model")
     parser.add_argument(
         "--lr-scheduler",
         default='piecewise',