polish Optimizer's API description, test=develop (#22314)

python/paddle/fluid/optimizer.py

@@ -123,7 +123,11 @@ class Optimizer(object):
             .. code-block:: python
 
                 import paddle.fluid as fluid
-                adam = fluid.optimizer.Adam(0.001)
+
+                with fluid.dygraph.guard():
+                    emb = fluid.dygraph.Embedding([10, 10])
+
+                    adam = fluid.optimizer.Adam(0.001, parameter_list=emb.parameters())
                     state_dict = adam.state_dict()
 
         '''
@@ -160,19 +164,19 @@ class Optimizer(object):
             .. code-block:: python
 
                 with fluid.dygraph.guard():
-                    emb = fluid.dygraph.Embedding( "emb", [10, 10])
+                    emb = fluid.dygraph.Embedding([10, 10])
 
                     state_dict = emb.state_dict()
-                    fluid.save_dygraph( state_dict, "paddle_dy")
+                    fluid.save_dygraph(state_dict, "paddle_dy")
 
-                    adam = fluid.optimizer.Adam( learning_rate = fluid.layers.noam_decay( 100, 10000), 
-                                                 parameter_list = emb.parameters() )
+                    adam = fluid.optimizer.Adam(learning_rate=fluid.layers.noam_decay( 100, 10000), 
+                                                parameter_list=emb.parameters())
                     state_dict = adam.state_dict()
-                    fluid.save_dygraph( state_dict, "padle_dy")
+                    fluid.save_dygraph(state_dict, "paddle_dy")
 
                     para_state_dict, opti_state_dict = fluid.load_dygraph( "paddle_dy")
 
-                    adam.set_dict( opti_state_dict )
+                    adam.set_dict(opti_state_dict)
 
         '''