Simplify fluid api for fit a line (#10301)

python/paddle/fluid/tests/book/high-level-api/CMakeLists.txt

@@ -6,4 +6,5 @@ foreach(src ${TEST_OPS})
     py_test(${src} SRCS ${src}.py)
 endforeach()
 
+add_subdirectory(fit_a_line)
 add_subdirectory(recognize_digits)

python/paddle/fluid/tests/book/high-level-api/fit_a_line/CMakeLists.txt

@@ -0,0 +1,7 @@
+file(GLOB TEST_OPS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" "test_*.py")
+string(REPLACE ".py" "" TEST_OPS "${TEST_OPS}")
+
+# default test
+foreach(src ${TEST_OPS})
+    py_test(${src} SRCS ${src}.py)
+endforeach()

python/paddle/fluid/tests/book/high-level-api/fit_a_line/test_fit_a_line.py

@@ -0,0 +1,137 @@
+#   Copyright (c) 2018 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 paddle
+import paddle.fluid as fluid
+import contextlib
+import numpy
+import unittest
+
+# train reader
+BATCH_SIZE = 20
+
+train_reader = paddle.batch(
+    paddle.reader.shuffle(
+        paddle.dataset.uci_housing.train(), buf_size=500),
+    batch_size=BATCH_SIZE)
+
+test_reader = paddle.batch(
+    paddle.reader.shuffle(
+        paddle.dataset.uci_housing.test(), buf_size=500),
+    batch_size=BATCH_SIZE)
+
+
+def inference_program():
+    x = fluid.layers.data(name='x', shape=[13], dtype='float32')
+    y_predict = fluid.layers.fc(input=x, size=1, act=None)
+    return y_predict
+
+
+def linear():
+    y = fluid.layers.data(name='y', shape=[1], dtype='float32')
+    y_predict = inference_program()
+
+    loss = fluid.layers.square_error_cost(input=y_predict, label=y)
+    avg_loss = fluid.layers.mean(loss)
+
+    return avg_loss
+
+
+def train(use_cuda, save_dirname):
+    place = fluid.CUDAPlace(0) if use_cuda else fluid.CPUPlace()
+
+    trainer = fluid.Trainer(
+        train_func=linear,
+        infer_func=inference_program,
+        place=place,
+        optimizer=fluid.optimizer.SGD(learning_rate=0.001))
+
+    def event_handler(event):
+        if isinstance(event, fluid.EndEpochEvent):
+            test_metrics = trainer.test(
+                reader=test_reader, feed_order=['x', 'y'])
+            print test_metrics
+            '''
+            
+            ...
+            ['25.768919467926025']
+            ['15.343549569447836']
+            ...
+            
+            '''
+            if float(test_metrics[0]) < 20.0:
+                if save_dirname is not None:
+                    # NOT clear yet
+                    # fluid.io.save_inference_model(save_dirname, ['x'], [y_predict])
+                    # trainer.save_params(save_dirname)
+                    # https://github.com/PaddlePaddle/Paddle/pull/10445
+                    trainer.save_inference_model(save_dirname)
+            return
+
+    trainer.train(
+        reader=train_reader,
+        num_epochs=100,
+        event_handler=event_handler,
+        feed_order=['x', 'y'])
+
+
+# infer
+def infer(use_cuda, save_dirname=None):
+    if save_dirname is None:
+        return
+
+    place = fluid.CUDAPlace(0) if use_cuda else fluid.CPUPlace()
+    inferencer = fluid.Inferencer(param_path=save_dirname, place=place)
+
+    batch_size = 10
+    tensor_x = numpy.random.uniform(0, 10, [batch_size, 13]).astype("float32")
+
+    results = inferencer.infer({'x': tensor_x})
+    print("infer results: ", results[0])
+
+
+def main(use_cuda):
+    if use_cuda and not fluid.core.is_compiled_with_cuda():
+        return
+
+    # Directory for saving the trained model
+    save_dirname = "fit_a_line.inference.model"
+
+    train(use_cuda, save_dirname)
+    infer(use_cuda, save_dirname)
+
+
+class TestFitALine(unittest.TestCase):
+    def test_cpu(self):
+        with self.program_scope_guard():
+            with fluid.unique_name.guard():
+                main(use_cuda=False)
+
+    def test_cuda(self):
+        with self.program_scope_guard():
+            with fluid.unique_name.guard():
+                main(use_cuda=True)
+
+    @contextlib.contextmanager
+    def program_scope_guard(self):
+        prog = fluid.Program()
+        startup_prog = fluid.Program()
+        scope = fluid.core.Scope()
+        with fluid.scope_guard(scope):
+            with fluid.program_guard(prog, startup_prog):
+                yield
+
+
+if __name__ == '__main__':
+    unittest.main()