test=document, bug fix for LookaheadOptimizer and LarsMomentumOptimzer (#2249)

doc/fluid/api_cn/optimizer_cn/LarsMomentumOptimizer_cn.rst

@@ -38,6 +38,7 @@ LarsMomentumOptimizer
 .. code-block:: python
 
     import paddle.fluid as fluid
+    import numpy as np
 
     np_inp = np.array([[1.0, 2.0], [3.0, 4.0]], dtype=np.float32)
     inp = fluid.layers.data(

doc/fluid/api_cn/optimizer_cn/LookaheadOptimizer_cn.rst

@@ -29,7 +29,7 @@ LookaheadOptimizer
 
             import paddle
             import paddle.fluid as fluid
-            import numpy as np
+            import numpy.random as random
 
             x = fluid.layers.data(name='x', shape=[2], dtype='float32')
             label = fluid.layers.data(name="label", shape=[1], dtype="int64")
@@ -46,11 +46,14 @@ LookaheadOptimizer
             exe = fluid.Executor(place)
             exe.run(fluid.default_startup_program())
 
+            def train_reader(limit=5):
+                for i in range(limit):
+                    yield random.random([2]).astype('float32'), random.random([1]).astype('int64')
+            
             feeder = fluid.DataFeeder(feed_list=[x, label], place=place)
-
-            step = 0
-            while(step < 10):
-                step += 1
+            reader = paddle.batch(paddle.reader.shuffle(train_reader, buf_size=50000),batch_size=1)
+            
+            for batch_data in reader():
                 exe.run(fluid.default_main_program(),
                 feed=feeder.feed(batch_data))