Trainer documentation

python/paddle/fluid/trainer.py

@@ -151,11 +151,62 @@ def check_and_get_place(place):
 
 class Trainer(object):
     """
+    A trainer wraps MultiGPU/MultiNode training loops and can be used to train a
+    simple neural network easily.
+
+    This API takes a :code:`train_func`. A :code:`train_func` is a function that
+    return loss as it first return value. The reset value can be fetched by
+    EndStepEvent.metrics
+
+    This API also takes a :code:`optimizer_func` that will return an optimizer
+    instance.
+
+    For example, to train a MLP for MNIST dataset, the sample program is
+
+    >>> import paddle.fluid as fluid
+    >>>
+    >>> def mlp(image, layer_sizes=[200, 100], activation="relu", num_classes=10):
+    >>>     hidden = image
+    >>>     for layer_size in layer_sizes:
+    >>>         hidden = fluid.layers.fc(input=hidden, size=layer_size, act=activation)
+    >>>     return fluid.layers.fc(input=hidden, size=num_classes, act="softmax")
+    >>>
+    >>> def train_mnist_mlp():
+    >>>     img = fluid.layers.data(name='image', shape=[784])
+    >>>     label = fluid.layers.data(name='label', shape=[1], dtype='int64')
+    >>>     prediction = mlp(img)
+    >>>     return fluid.layers.mean(fluid.layers.cross_entropy(prediction, label))
+    >>>
+    >>> def optimizer():
+    >>>     return fluid.optimizer.Adam()
+    >>>
+    >>> trainer = Trainer(train_func=train_mnist_mlp,
+    >>>                   optimizer_func=optimizer,
+    >>>                   place=fluid.CUDAPlace(0),
+    >>>                   parallel=True)
+    >>>
+    >>> def train_callback(event):
+    >>>     if isinstance(event, fluid.EndStepEvent):
+    >>>         print "Epoch ID", event.epoch, "Step ID",\
+    >>>             event.step, "AvgLoss", event.metrics[0]
+    >>>     elif isinstance(event, fluid.EndEpochEvent):
+    >>>         trainer.save_params("./model_{0}".format(event.epoch))
+    >>>
+    >>> trainer.train(num_epochs=100, event_handler=train_callback)
+
+    For more example, please see :ref:`api_guide_high_level_api`.
+
 
     Args:
-        train_func(callable): A function which will return loss. The loss must be a scalar.
+        train_func(callable): A function which will return loss. The loss must be
+            a scalar tensor.
         optimizer_func(callable): A function that returns an Optimizer object.
-        place: The device place of this trainer.
+        place(CUDAPlace|CPUPlace): The device place of this trainer. If
+            :code:`parallel=True,` all CUDA Places will be used if :code:`place`
+            is a :code:`CUDAPlace`.
+        parallel(bool): True if use multiple devices.
+        checkpoint_config(CheckpointConfig): Configuration about how to save
+            checkpoints.
     """
 
     def __init__(self,
@@ -167,9 +218,6 @@ class Trainer(object):
                  checkpoint_config=None):
         self.__stop = False
         self.parallel = parallel
-        # 1. we need to generate a framework.Program by calling
-        # program_func. Reference: fluid.program_guard in
-        # test_word2vec.py
 
         # config for checkpoint
         # only chief worker will save variables
@@ -183,6 +231,10 @@ class Trainer(object):
 
         self.scope = core.Scope()
 
+        # 1. we need to generate a framework.Program by calling
+        # program_func. Reference: fluid.program_guard in
+        # test_word2vec.py
+
         self.startup_program = framework.Program()
         self.train_program = framework.Program()
 
@@ -315,17 +367,18 @@ class Trainer(object):
 
     def train(self, num_epochs, event_handler, reader=None, feed_order=None):
         """
-        Train the model.
+        Start the train loop to train the model.
 
         Args:
             num_epochs: The number of epoch. An epoch will process all data in reader
             event_handler: The event handler. A function with type (ev:Event)->void
-            reader:
+            reader: A reader creator object. See also
+                :ref:`api_guide_python_reader` .
             feed_order: Feeding order of reader. None will following the defining
                 order in program
 
         Returns:
-
+            None
         """
         training_role = os.getenv("PADDLE_TRAINING_ROLE", "")
         if training_role == "PSERVER":
@@ -354,7 +407,14 @@ class Trainer(object):
                                       self.train_func_outputs)
 
     def save_params(self, param_path):
-        # reference: save_persistables in io.py
+        """
+        Save all parameters into :code:`param_path`
+        Args:
+            param_path(str): The path to save parameters
+
+        Returns:
+            None
+        """
         with self._prog_and_scope_guard():
             exe = executor.Executor(self.place)
             io.save_persistables(exe, dirname=param_path)