official/mnist: Use tf.keras.Sequential to simplify network definition.

official/mnist/mnist.py

@@ -29,7 +29,7 @@ from official.utils.logs import hooks_helper
 LEARNING_RATE = 1e-4
 
 
-class Model(tf.keras.Model):
+def create_model(data_format):
   """Model to recognize digits in the MNIST dataset.
 
   Network structure is equivalent to:
@@ -37,60 +37,41 @@ class Model(tf.keras.Model):
   and
   https://github.com/tensorflow/models/blob/master/tutorials/image/mnist/convolutional.py
 
-  But written as a tf.keras.Model using the tf.layers API.
-  """
+  But uses the tf.keras API.
+
+  Args:
+    data_format: Either 'channels_first' or 'channels_last'.
+      'channels_first' is typically faster on GPUs while 'channels_last' is
+      typically faster on CPUs. See
+      https://www.tensorflow.org/performance/performance_guide#data_formats
 
-  def __init__(self, data_format):
-    """Creates a model for classifying a hand-written digit.
-
-    Args:
-      data_format: Either 'channels_first' or 'channels_last'.
-        'channels_first' is typically faster on GPUs while 'channels_last' is
-        typically faster on CPUs. See
-        https://www.tensorflow.org/performance/performance_guide#data_formats
-    """
-    super(Model, self).__init__()
-    if data_format == 'channels_first':
-      self._input_shape = [-1, 1, 28, 28]
-    else:
-      assert data_format == 'channels_last'
-      self._input_shape = [-1, 28, 28, 1]
-
-    self.conv1 = tf.layers.Conv2D(
-        32, 5, padding='same', data_format=data_format, activation=tf.nn.relu)
-    self.conv2 = tf.layers.Conv2D(
-        64, 5, padding='same', data_format=data_format, activation=tf.nn.relu)
-    self.fc1 = tf.layers.Dense(1024, activation=tf.nn.relu)
-    self.fc2 = tf.layers.Dense(10)
-    self.dropout = tf.layers.Dropout(0.4)
-    self.max_pool2d = tf.layers.MaxPooling2D(
-        (2, 2), (2, 2), padding='same', data_format=data_format)
-
-  def __call__(self, inputs, training):
-    """Add operations to classify a batch of input images.
-
-    Args:
-      inputs: A Tensor representing a batch of input images.
-      training: A boolean. Set to True to add operations required only when
-        training the classifier.
-
-    Returns:
-      A logits Tensor with shape [<batch_size>, 10].
-    """
-    y = tf.reshape(inputs, self._input_shape)
-    y = self.conv1(y)
-    y = self.max_pool2d(y)
-    y = self.conv2(y)
-    y = self.max_pool2d(y)
-    y = tf.layers.flatten(y)
-    y = self.fc1(y)
-    y = self.dropout(y, training=training)
-    return self.fc2(y)
+  Returns:
+    A tf.keras.Model.
+  """
+  input_shape = None
+  if data_format == 'channels_first':
+    input_shape = [1, 28, 28]
+  else:
+    assert data_format == 'channels_last'
+    input_shape = [28, 28, 1]
+
+  L = tf.keras.layers
+  max_pool = L.MaxPooling2D((2, 2), (2, 2), padding='same', data_format=data_format)
+  return tf.keras.Sequential([
+      L.Reshape(input_shape),
+      L.Conv2D(32, 5, padding='same', data_format=data_format, activation=tf.nn.relu),
+      max_pool,
+      L.Conv2D(64, 5, padding='same', data_format=data_format, activation=tf.nn.relu),
+      max_pool,
+      L.Flatten(),
+      L.Dense(1024, activation=tf.nn.relu),
+      L.Dropout(0.4),
+      L.Dense(10)])
 
 
 def model_fn(features, labels, mode, params):
   """The model_fn argument for creating an Estimator."""
-  model = Model(params['data_format'])
+  model = create_model(params['data_format'])
   image = features
   if isinstance(image, dict):
     image = features['image']

official/mnist/mnist_eager.py

@@ -116,7 +116,7 @@ def main(argv):
   test_ds = mnist_dataset.test(flags.data_dir).batch(flags.batch_size)
 
   # Create the model and optimizer
-  model = mnist.Model(data_format)
+  model = mnist.create_model(data_format)
   optimizer = tf.train.MomentumOptimizer(flags.lr, flags.momentum)
 
   # Create file writers for writing TensorBoard summaries.

official/mnist/mnist_eager_test.py

@@ -40,7 +40,7 @@ def random_dataset():
 
 
 def train(defun=False):
-  model = mnist.Model(data_format())
+  model = mnist.create_model(data_format())
   if defun:
     model.call = tfe.defun(model.call)
   optimizer = tf.train.GradientDescentOptimizer(learning_rate=0.01)
@@ -51,7 +51,7 @@ def train(defun=False):
 
 
 def evaluate(defun=False):
-  model = mnist.Model(data_format())
+  model = mnist.create_model(data_format())
   dataset = random_dataset()
   if defun:
     model.call = tfe.defun(model.call)

official/mnist/mnist_tpu.py

@@ -86,7 +86,7 @@ def model_fn(features, labels, mode, params):
   if isinstance(image, dict):
     image = features["image"]
 
-  model = mnist.Model("channels_last")
+  model = mnist.create_model("channels_last")
   logits = model(image, training=(mode == tf.estimator.ModeKeys.TRAIN))
   loss = tf.losses.sparse_softmax_cross_entropy(labels=labels, logits=logits)