Add API docs.

Author: panyx0718

paddle/fluid/operators/get_places_op.cc

@@ -85,7 +85,7 @@ class GetPlacesOpProtoMaker : public framework::OpProtoAndCheckerMaker {
         .InEnum({"CUDA", "CPU", "AUTO"})
         .SetDefault("AUTO");
     AddComment(R"DOC(
-Returns a list of places based on flags. The list will be used for parallel
+Returns a list of places based on arguments. The list will be used for parallel
 execution.
 )DOC");
   }

python/paddle/fluid/layers/control_flow.py

@@ -1209,6 +1209,32 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 
 
 class IfElse(object):
+    """
+    if-else control flow.
+
+    Args:
+        cond (Variable): condition used to compare.
+        name (str, default None): The name of this layer.
+
+    Examples:
+          .. code-block:: python
+            limit = layers.fill_constant_batch_size_like(
+                input=label, dtype='int64', shape=[1], value=5.0)
+            cond = layers.less_than(x=label, y=limit)
+            ie = layers.IfElse(cond)
+            with ie.true_block():
+                true_image = ie.input(image)
+                hidden = layers.fc(input=true_image, size=100, act='tanh')
+                prob = layers.fc(input=hidden, size=10, act='softmax')
+                ie.output(prob)
+
+            with ie.false_block():
+                false_image = ie.input(image)
+                hidden = layers.fc(input=false_image, size=200, act='tanh')
+                prob = layers.fc(input=hidden, size=10, act='softmax')
+                ie.output(prob)
+            prob = ie()
+    """
     OUT_IF_ELSE_BLOCKS = 0
     IN_IF_ELSE_TRUE_BLOCKS = 1
     IN_IF_ELSE_FALSE_BLOCKS = 2

python/paddle/fluid/layers/io.py

@@ -587,6 +587,25 @@ def read_file(file_obj):
 
 
 class Preprocessor(object):
+    """
+    A block for data pre-processing in reader.
+
+    Args:
+        reader (Variable): A reader variable.
+        name (str, default None): The name of the reader.
+
+    Examples:
+          .. code-block:: python
+            preprocessor = fluid.layers.io.Preprocessor(reader=reader)
+            with preprocessor.block():
+                img, lbl = preprocessor.inputs()
+                img_out = img / 2
+                lbl_out = lbl + 1
+                preprocessor.outputs(img_out, lbl_out)
+
+            data_file = fluid.layers.io.double_buffer(preprocessor())
+
+    """
     BEFORE_SUB_BLOCK = 0
     IN_SUB_BLOCK = 1
     AFTER_SUB_BLOCK = 2