Save and restore models

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Model progress can be saved during—and after—training. This means a model can resume where it left off and avoid long training times. Saving also means you can share your model and others can recreate your work. When publishing research models and techniques, most machine learning practitioners share:

  • code to create the model, and
  • the trained weights, or parameters, for the model

Sharing this data helps others understand how the model works and try it themselves with new data.

Options

There are different ways to save TensorFlow models—depending on the API you're using. This guide uses tf.keras, a high-level API to build and train models in TensorFlow. For other approaches, see the TensorFlow Save and Restore guide or Saving in eager.

Setup

Installs and imports

Install and import TensorFlow and dependencies:

!pip install -q h5py pyyaml 

Get an example dataset

We'll use the MNIST dataset to train our model to demonstrate saving weights. To speed up these demonstration runs, only use the first 1000 examples:

from __future__ import absolute_import, division, print_function

import os

import tensorflow as tf
from tensorflow import keras

tf.__version__
'1.10.0'
(train_images, train_labels), (test_images, test_labels) = tf.keras.datasets.mnist.load_data()

train_labels = train_labels[:1000]
test_labels = test_labels[:1000]

train_images = train_images[:1000].reshape(-1, 28 * 28) / 255.0
test_images = test_images[:1000].reshape(-1, 28 * 28) / 255.0
Downloading data from https://storage.googleapis.com/tensorflow/tf-keras-datasets/mnist.npz
11493376/11490434 [==============================] - 0s 0us/step

Define a model

Let's build a simple model we'll use to demonstrate saving and loading weights.

# Returns a short sequential model
def create_model():
  model = tf.keras.models.Sequential([
    keras.layers.Dense(512, activation=tf.nn.relu, input_shape=(784,)),
    keras.layers.Dropout(0.2),
    keras.layers.Dense(10, activation=tf.nn.softmax)
  ])
  
  model.compile(optimizer=tf.keras.optimizers.Adam(), 
                loss=tf.keras.losses.sparse_categorical_crossentropy,
                metrics=['accuracy'])
  
  return model


# Create a basic model instance
model = create_model()
model.summary()
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
dense (Dense)                (None, 512)               401920    
_________________________________________________________________
dropout (Dropout)            (None, 512)               0         
_________________________________________________________________
dense_1 (Dense)              (None, 10)                5130      
=================================================================
Total params: 407,050
Trainable params: 407,050
Non-trainable params: 0
_________________________________________________________________

Save checkpoints during training

The primary use case is to automatically save checkpoints during and at the end of training. This way you can use a trained model without having to retrain it, or pick-up training where you left of—in case the training process was interrupted.

tf.keras.callbacks.ModelCheckpoint is a callback that performs this task. The callback takes a couple of arguments to configure checkpointing.

Checkpoint callback usage

Train the model and pass it the ModelCheckpoint callback:

checkpoint_path = "training_1/cp.ckpt"
checkpoint_dir = os.path.dirname(checkpoint_path)

# Create checkpoint callback
cp_callback = tf.keras.callbacks.ModelCheckpoint(checkpoint_path, 
                                                 save_weights_only=True,
                                                 verbose=1)

model = create_model()

model.fit(train_images, train_labels,  epochs = 10, 
          validation_data = (test_images,test_labels),
          callbacks = [cp_callback])  # pass callback to training
Train on 1000 samples, validate on 1000 samples
Epoch 1/10
1000/1000 [==============================] - 0s 397us/step - loss: 1.1368 - acc: 0.6780 - val_loss: 0.7005 - val_acc: 0.7780

Epoch 00001: saving model to training_1/cp.ckpt
Epoch 2/10
1000/1000 [==============================] - 0s 138us/step - loss: 0.4152 - acc: 0.8810 - val_loss: 0.5274 - val_acc: 0.8350

Epoch 00002: saving model to training_1/cp.ckpt
Epoch 3/10
1000/1000 [==============================] - 0s 123us/step - loss: 0.2921 - acc: 0.9190 - val_loss: 0.4760 - val_acc: 0.8450

Epoch 00003: saving model to training_1/cp.ckpt
Epoch 4/10
1000/1000 [==============================] - 0s 121us/step - loss: 0.2084 - acc: 0.9530 - val_loss: 0.4468 - val_acc: 0.8470

Epoch 00004: saving model to training_1/cp.ckpt
Epoch 5/10
1000/1000 [==============================] - 0s 121us/step - loss: 0.1490 - acc: 0.9700 - val_loss: 0.4204 - val_acc: 0.8610

Epoch 00005: saving model to training_1/cp.ckpt
Epoch 6/10
1000/1000 [==============================] - 0s 116us/step - loss: 0.1160 - acc: 0.9770 - val_loss: 0.4394 - val_acc: 0.8530

Epoch 00006: saving model to training_1/cp.ckpt
Epoch 7/10
1000/1000 [==============================] - 0s 118us/step - loss: 0.0880 - acc: 0.9870 - val_loss: 0.4297 - val_acc: 0.8590

Epoch 00007: saving model to training_1/cp.ckpt
Epoch 8/10
1000/1000 [==============================] - 0s 126us/step - loss: 0.0710 - acc: 0.9910 - val_loss: 0.3954 - val_acc: 0.8690

Epoch 00008: saving model to training_1/cp.ckpt
Epoch 9/10
1000/1000 [==============================] - 0s 121us/step - loss: 0.0535 - acc: 0.9970 - val_loss: 0.4215 - val_acc: 0.8630

Epoch 00009: saving model to training_1/cp.ckpt
Epoch 10/10
1000/1000 [==============================] - 0s 125us/step - loss: 0.0426 - acc: 0.9980 - val_loss: 0.4083 - val_acc: 0.8690

Epoch 00010: saving model to training_1/cp.ckpt

This creates a single collection of TensorFlow checkpoint files that are updated at the end of each epoch:

!ls {checkpoint_dir}
checkpoint  cp.ckpt.data-00000-of-00001  cp.ckpt.index

Create a new, untrained model. When restoring a model from only weights, you must have a model with the same architecture as the original model. Since it's the same model architecture, we can share weights despite that it's a different instance of the model.

Now rebuild a fresh, untrained model, and evaluate it on the test set. An untrained model will perform at chance levels (~10% accuracy):

model = create_model()

loss, acc = model.evaluate(test_images, test_labels)
print("Untrained model, accuracy: {:5.2f}%".format(100*acc))
1000/1000 [==============================] - 0s 91us/step
Untrained model, accuracy: 13.80%

Then load the weights from the checkpoint, and re-evaluate:

model.load_weights(checkpoint_path)
loss,acc = model.evaluate(test_images, test_labels)
print("Restored model, accuracy: {:5.2f}%".format(100*acc))
1000/1000 [==============================] - 0s 26us/step
Restored model, accuracy: 86.90%

Checkpoint callback options

The callback provides several options to give the resulting checkpoints unique names, and adjust the checkpointing frequency.

Train a new model, and save uniquely named checkpoints once every 5-epochs:

# include the epoch in the file name. (uses `str.format`)
checkpoint_path = "training_2/cp-{epoch:04d}.ckpt"
checkpoint_dir = os.path.dirname(checkpoint_path)

cp_callback = tf.keras.callbacks.ModelCheckpoint(
    checkpoint_path, verbose=1, save_weights_only=True,
    # Save weights, every 5-epochs.
    period=5)

model = create_model()
model.fit(train_images, train_labels,
          epochs = 50, callbacks = [cp_callback],
          validation_data = (test_images,test_labels),
          verbose=0)

Epoch 00005: saving model to training_2/cp-0005.ckpt

Epoch 00010: saving model to training_2/cp-0010.ckpt

Epoch 00015: saving model to training_2/cp-0015.ckpt

Epoch 00020: saving model to training_2/cp-0020.ckpt

Epoch 00025: saving model to training_2/cp-0025.ckpt

Epoch 00030: saving model to training_2/cp-0030.ckpt

Epoch 00035: saving model to training_2/cp-0035.ckpt

Epoch 00040: saving model to training_2/cp-0040.ckpt

Epoch 00045: saving model to training_2/cp-0045.ckpt

Epoch 00050: saving model to training_2/cp-0050.ckpt

Now, have a look at the resulting checkpoints (sorting by modification date):

import pathlib

# Sort the checkpoints by modification time.
checkpoints = pathlib.Path(checkpoint_dir).glob("*.index")
checkpoints = sorted(checkpoints, key=lambda cp:cp.stat().st_mtime)
checkpoints = [cp.with_suffix('') for cp in checkpoints]
latest = str(checkpoints[-1])
checkpoints
[PosixPath('training_2/cp-0030.ckpt'),
 PosixPath('training_2/cp-0035.ckpt'),
 PosixPath('training_2/cp-0040.ckpt'),
 PosixPath('training_2/cp-0045.ckpt'),
 PosixPath('training_2/cp-0050.ckpt')]

To test, reset the model and load the latest checkpoint:

model = create_model()
model.load_weights(latest)
loss, acc = model.evaluate(test_images, test_labels)
print("Restored model, accuracy: {:5.2f}%".format(100*acc))
1000/1000 [==============================] - 0s 52us/step
Restored model, accuracy: 87.30%

What are these files?

The above code stores the weights to a collection of checkpoint-formatted files that contain only the trained weights in a binary format. Checkpoints contain: * One or more shards that contain your model's weights. * An index file that indicates which weights are stored in a which shard.

If you are only training a model on a single machine, you'll have one shard with the suffix: .data-00000-of-00001

Manually save weights

Above you saw how to load the weights into a model.

Manually saving the weights is just as simple, use the Model.save_weights method.

# Save the weights
model.save_weights('./checkpoints/my_checkpoint')

# Restore the weights
model = create_model()
model.load_weights('./checkpoints/my_checkpoint')

loss,acc = model.evaluate(test_images, test_labels)
print("Restored model, accuracy: {:5.2f}%".format(100*acc))
1000/1000 [==============================] - 0s 102us/step
Restored model, accuracy: 87.30%

Save the entire model

The entire model can be saved to a file that contains the weight values, the model's configuration, and even the optimizer's configuration. This allows you to checkpoint a model and resume training later—from the exact same state—without access to the original code.

Saving a fully-functional model in Keras is very useful—you can load them in TensorFlow.js and then train and run them in web browsers.

Keras provides a basic save format using the HDF5 standard. For our purposes, the saved model can be treated as a single binary blob.

model = create_model()

model.fit(train_images, train_labels, epochs=5)

# Save entire model to a HDF5 file
model.save('my_model.h5')
Epoch 1/5
1000/1000 [==============================] - 0s 313us/step - loss: 1.1640 - acc: 0.6550
Epoch 2/5
1000/1000 [==============================] - 0s 109us/step - loss: 0.4138 - acc: 0.8850
Epoch 3/5
1000/1000 [==============================] - 0s 110us/step - loss: 0.3034 - acc: 0.9220
Epoch 4/5
1000/1000 [==============================] - 0s 108us/step - loss: 0.2302 - acc: 0.9390
Epoch 5/5
1000/1000 [==============================] - 0s 110us/step - loss: 0.1491 - acc: 0.9710

Now recreate the model from that file:

# Recreate the exact same model, including weights and optimizer.
new_model = keras.models.load_model('my_model.h5')
new_model.summary()
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
dense_12 (Dense)             (None, 512)               401920    
_________________________________________________________________
dropout_6 (Dropout)          (None, 512)               0         
_________________________________________________________________
dense_13 (Dense)             (None, 10)                5130      
=================================================================
Total params: 407,050
Trainable params: 407,050
Non-trainable params: 0
_________________________________________________________________

Check its accuracy:

loss, acc = new_model.evaluate(test_images, test_labels)
print("Restored model, accuracy: {:5.2f}%".format(100*acc))
1000/1000 [==============================] - 0s 80us/step
Restored model, accuracy: 86.10%

This technique saves everything:

  • The weight values
  • The model's configuration(architecture)
  • The optimizer configuration

Keras saves models by inspecting the architecture. Currently, it is not able to save TensorFlow optimizers (from tf.train). When using those you will need to re-compile the model after loading, and you will loose the state of the optimizer.

What's Next

That was a quick guide to saving and loading in with tf.keras.

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