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Exporting an MNIST Classifier in SavedModel Format

In this exercise, we will learn on how to create models for TensorFlow Hub. You will be tasked with performing the following tasks:

  • Creating a simple MNIST classifier and evaluating its accuracy.
  • Exporting it into SavedModel.
  • Hosting the model as TF Hub Module.
  • Importing this TF Hub Module to be used with Keras Layers.
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import numpy as np
import tensorflow as tf
import tensorflow_hub as hub
import tensorflow_datasets as tfds

from os import getcwd

Create an MNIST Classifier

We will start by creating a class called MNIST. This class will load the MNIST dataset, preprocess the images from the dataset, and build a CNN based classifier. This class will also have some methods to train, test, and save our model.

In the cell below, fill in the missing code and create the following Keras Sequential model:

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Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
lambda (Lambda)              (None, 28, 28, 1)         0         
_________________________________________________________________
conv2d (Conv2D)              (None, 28, 28, 8)         80        
_________________________________________________________________
max_pooling2d (MaxPooling2D) (None, 14, 14, 8)         0         
_________________________________________________________________
conv2d_1 (Conv2D)            (None, 14, 14, 16)        1168      
_________________________________________________________________
max_pooling2d_1 (MaxPooling2 (None, 7, 7, 16)          0         
_________________________________________________________________
conv2d_2 (Conv2D)            (None, 7, 7, 32)          4640      
_________________________________________________________________
flatten (Flatten)            (None, 1568)              0         
_________________________________________________________________
dense (Dense)                (None, 128)               200832    
_________________________________________________________________
dense_1 (Dense)              (None, 10)                1290      
=================================================================

Notice that we are using a tf.keras.layers.Lambda layer at the beginning of our model. Lambda layers are used to wrap arbitrary expressions as a Layer object:

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tf.keras.layers.Lambda(expression)

The Lambda layer exists so that arbitrary TensorFlow functions can be used when constructing Sequential and Functional API models. Lambda layers are best suited for simple operations. 

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class MNIST:
    def __init__(self, export_path, buffer_size=1000, batch_size=32,
                 learning_rate=1e-3, epochs=10):
        self._export_path = export_path
        self._buffer_size = buffer_size
        self._batch_size = batch_size
        self._learning_rate = learning_rate
        self._epochs = epochs
    
        self._build_model()
        self.train_dataset, self.test_dataset = self._prepare_dataset()
    
    # Function to preprocess the images.
    def preprocess_fn(self, x):
        
        # EXERCISE: Cast x to tf.float32 using the tf.cast() function.
        # You should also normalize the values of x to be in the range [0, 1].
        x = tf.cast(x, tf.float32) / 255.0
            
        return x
        
    def _build_model(self):
        
        # EXERCISE: Build the model according to the model summary shown above.
        self._model = tf.keras.models.Sequential([
            tf.keras.layers.Input(shape=(28, 28, 1), dtype=tf.uint8),
            
            # Use a Lambda layer to use the self.preprocess_fn function
            # defined above to preprocess the images.
            # YOUR CODE HERE
            tf.keras.layers.Lambda(self.preprocess_fn),
            
            # Create a Conv2D layer with 8 filters, a kernel size of 3
            # and padding='same'.
            # YOUR CODE HERE
            tf.keras.layers.Conv2D(filters = 8, kernel_size=3, padding="same"),
            
            # Create a MaxPool2D() layer. Use default values.
            # YOUR CODE HERE
            tf.keras.layers.MaxPool2D(),
            
            # Create a Conv2D layer with 16 filters, a kernel size of 3
            # and padding='same'.
            # YOUR CODE HERE
            tf.keras.layers.Conv2D(filters = 16, kernel_size=3, padding="same"),
            
            # Create a MaxPool2D() layer. Use default values.
            # YOUR CODE HERE
            tf.keras.layers.MaxPool2D(),
            
            # Create a Conv2D layer with 32 filters, a kernel size of 3
            # and padding='same'.
            # YOUR CODE HERE
            tf.keras.layers.Conv2D(filters = 32, kernel_size=3, padding="same"),
            
            # Create the Flatten and Dense layers as described in the 
            # model summary shown above.
            # YOUR CODE HERE
            
            tf.keras.layers.Flatten(),
            tf.keras.layers.Dense(128),
            tf.keras.layers.Dense(10, activation="softmax")
        ])
        
        # EXERCISE: Define the optimizer, loss function and metrics.
        
        # Use the tf.keras.optimizers.Adam optimizer and set the
        # learning rate to self._learning_rate.
        optimizer_fn = tf.keras.optimizers.Adam(learning_rate=self._learning_rate)
        
        # Use sparse_categorical_crossentropy as your loss function.
        loss_fn = "sparse_categorical_crossentropy"
        
        # Set the metrics to accuracy.
        metrics_list = ["accuracy"]
     
        # Compile the model.
        self._model.compile(optimizer_fn, loss=loss_fn, metrics=metrics_list)
        
        
    def _prepare_dataset(self):
        
        filePath = f"{getcwd()}/../tmp2"
        
        # EXERCISE: Load the MNIST dataset using tfds.load(). Make sure to use
        # the argument data_dir=filePath. You should load the images as well
        # as their corresponding labels and load both the test and train splits.
        dataset = tfds.load('mnist', split=['train', 'test'], data_dir = filePath, as_supervised=True)
        
        # EXERCISE: Extract the 'train' and 'test' splits from the dataset above.
        train_dataset, test_dataset = dataset
        
        return train_dataset, test_dataset
    
    def train(self):
        
        # EXERCISE: Shuffle and batch the self.train_dataset. Use self._buffer_size
        # as the shuffling buffer and self._batch_size as the batch size for batching. 
        dataset_tr = self.train_dataset.shuffle(self._buffer_size).batch(self._batch_size)
        
#         images, labels = next(iter(dataset_tr)).items()
#         print(images[1].shape) # (32, 28, 28, 1)
             
        
        # Train the model for specified number of epochs.
        self._model.fit(dataset_tr, epochs=self._epochs)
        
    def test(self):
        
        # EXERCISE: Batch the self.test_dataset. Use a batch size of 32.
        dataset_te = self.test_dataset.batch(32)
        
        # Evaluate the dataset
        results = self._model.evaluate(dataset_te)
    
        # Print the metric values on which the model is being evaluated on.
        for name, value in zip(self._model.metrics_names, results):
            print("%s: %.3f" % (name, value))
            
    def export_model(self):
        # Save the model.
        tf.saved_model.save(self._model, self._export_path)

Train, Evaluate, and Save the Model

We will now use the MNIST class we created above to create an mnist object. When creating our mnist object we will use a dictionary to pass our training parameters. We will then call the train and export_model methods to train and save our model, respectively. Finally, we call the test method to evaluate our model after training.

NOTE: It will take about 12 minutes to train the model for 5 epochs.

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# Define the training parameters.
args = {'export_path': './saved_model',
        'buffer_size': 1000,
        'batch_size': 32,
        'learning_rate': 1e-3,
        'epochs': 5
}

# Create the mnist object. 
mnist = MNIST(**args)
print(mnist._model.summary())



# Train the model.
mnist.train()

# Save the model.
mnist.export_model()

# Evaluate the trained MNIST model.
mnist.test()
WARNING:absl:Found a different version 3.0.0 of dataset mnist in data_dir /tf/week2/../tmp2. Using currently defined version 1.0.0.


Model: "sequential_2"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
lambda_1 (Lambda)            (None, 28, 28, 1)         0         
_________________________________________________________________
conv2d_3 (Conv2D)            (None, 28, 28, 8)         80        
_________________________________________________________________
max_pooling2d_2 (MaxPooling2 (None, 14, 14, 8)         0         
_________________________________________________________________
conv2d_4 (Conv2D)            (None, 14, 14, 16)        1168      
_________________________________________________________________
max_pooling2d_3 (MaxPooling2 (None, 7, 7, 16)          0         
_________________________________________________________________
conv2d_5 (Conv2D)            (None, 7, 7, 32)          4640      
_________________________________________________________________
flatten_1 (Flatten)          (None, 1568)              0         
_________________________________________________________________
dense_1 (Dense)              (None, 128)               200832    
_________________________________________________________________
dense_2 (Dense)              (None, 10)                1290      
=================================================================
Total params: 208,010
Trainable params: 208,010
Non-trainable params: 0
_________________________________________________________________
None
Epoch 1/5
1875/1875 [==============================] - 135s 72ms/step - loss: 0.1548 - accuracy: 0.9532548 - accuracy: 0.95
Epoch 2/5
 563/1875 [========>.....................] - ETA: 1:36 - loss: 0.0868 - accuracy: 0.9733

Create a Tarball

The export_model method saved our model in the TensorFlow SavedModel format in the ./saved_model directory. The SavedModel format saves our model and its weights in various files and directories. This makes it difficult to distribute our model. Therefore, it is convenient to create a single compressed file that contains all the files and folders of our model. To do this, we will use the tar archiving program to create a tarball (similar to a Zip file) that contains our SavedModel.

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# Create a tarball from the SavedModel.
!tar -cz -f module.tar.gz -C ./saved_model .

Inspect the Tarball

We can uncompress our tarball to make sure it has all the files and folders from our SavedModel.

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# Inspect the tarball.
!tar -tf module.tar.gz
./
./variables/
./variables/variables.data-00001-of-00002
./variables/variables.data-00000-of-00002
./variables/variables.index
./saved_model.pb
./assets/

Simulate Server Conditions

Once we have verified our tarball, we can now simulate server conditions. In a normal scenario, we will fetch our TF Hub module from a remote server using the module’s handle. However, since this notebook cannot host the server, we will instead point the module handle to the directory where our SavedModel is stored. 

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!rm -rf ./module
!mkdir -p module
!tar xvzf module.tar.gz -C ./module
./
./variables/
./variables/variables.data-00001-of-00002
./variables/variables.data-00000-of-00002
./variables/variables.index
./saved_model.pb
./assets/

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# Define the module handle.
MODULE_HANDLE = './module'

Load the TF Hub Module

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# EXERCISE: Load the TF Hub module using the hub.load API.
model = hub.load(MODULE_HANDLE)

Test the TF Hub Module

We will now test our TF Hub module with images from the test split of the MNIST dataset.

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filePath = f"{getcwd()}/../tmp2"

# EXERCISE: Load the MNIST 'test' split using tfds.load().
# Make sure to use the argument data_dir=filePath. You
# should load the images along with their corresponding labels.

dataset = tfds.load('mnist', split=tfds.Split.TEST, data_dir = filePath, as_supervised=True)

# EXERCISE: Batch the dataset using a batch size of 32.
test_dataset = dataset.batch(32)
WARNING:absl:Found a different version 3.0.0 of dataset mnist in data_dir /tf/week2/../tmp2. Using currently defined version 1.0.0.

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# Test the TF Hub module for a single batch of data
for batch_data in test_dataset.take(1):
    outputs = model(batch_data[0])
    outputs = np.argmax(outputs, axis=-1)
    print('Predicted Labels:', outputs)
    print('True Labels:     ', batch_data[1].numpy())
Predicted Labels: [6 2 3 7 2 2 3 4 7 6 6 9 2 0 9 6 2 0 6 5 1 4 8 1 9 8 4 0 0 5 8 4]
True Labels:      [6 2 3 7 2 2 3 4 7 6 6 9 2 0 9 6 8 0 6 5 1 4 8 1 9 8 4 0 0 5 2 4]

We can see that the model correctly predicts the labels for most images in the batch.

Evaluate the Model Using Keras

In the cell below, you will integrate the TensorFlow Hub module into the high level Keras API.

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# EXERCISE: Integrate the TensorFlow Hub module into a Keras
# sequential model. You should use a hub.KerasLayer and you 
# should make sure to use the correct values for the output_shape,
# and input_shape parameters. You should also use tf.uint8 for
# the dtype parameter.

model = tf.keras.Sequential([
    hub.KerasLayer(model, output_shape=[10], input_shape=[28,28,1], 
                           dtype=tf.uint8)
]) 


# Compile the model.
model.compile(optimizer='adam',
              loss='sparse_categorical_crossentropy', 
              metrics=['accuracy'])
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# Evaluate the model on the test_dataset.
results = model.evaluate(test_dataset)
313/313 [==============================] - 27s 88ms/step - loss: 0.0605 - accuracy: 0.9824

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# Print the metric values on which the model is being evaluated on.
for name, value in zip(model.metrics_names, results):
    print("%s: %.3f" % (name, value))
loss: 0.061
accuracy: 0.982
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