give warnings when save a model without any parameters (#19931)

* give warnings when save a model without any parameters test=develop

* delete one line comment test=develop

python/paddle/fluid/io.py

@@ -217,6 +217,13 @@ def save_vars(executor,
             vars=list(filter(predicate, main_program.list_vars())),
             filename=filename)
     else:
+        # give warning when there is no var in model
+        if len(list(vars)) == 0:
+            warnings.warn(
+                "no variable in your model, please ensure there are any variables in your model to save"
+            )
+            return None
+
         save_program = Program()
         save_block = save_program.global_block()
 

python/paddle/fluid/tests/unittests/test_save_model_without_var.py

@@ -0,0 +1,57 @@
+# Copyright (c) 2019 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import numpy as np
+import warnings
+import unittest
+import paddle
+import paddle.fluid as fluid
+from paddle.fluid.layers.device import get_places
+from paddle.fluid.executor import as_numpy
+
+
+class TestSaveModelWithoutVar(unittest.TestCase):
+    def test_no_var_save(self):
+        data = fluid.layers.data(
+            name='data',
+            shape=[-1, 1],
+            dtype='float32',
+            append_batch_size=False)
+        data_plus = data + 1
+
+        if fluid.core.is_compiled_with_cuda():
+            place = fluid.core.CUDAPlace(0)
+        else:
+            place = fluid.core.CPUPlace()
+
+        exe = fluid.Executor(place)
+        exe.run(fluid.default_startup_program())
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+
+            fluid.io.save_inference_model(
+                dirname='test',
+                feeded_var_names=['data'],
+                target_vars=[data_plus],
+                executor=exe,
+                model_filename='model',
+                params_filename='params')
+            expected_warn = "no variable in your model, please ensure there are any variables in your model to save"
+            self.assertTrue(len(w) > 0)
+            self.assertTrue(expected_warn == str(w[0].message))
+
+
+if __name__ == '__main__':
+    unittest.main()