title: tensorflow keras save and load model
body: <p>I have run this example and I got the following error when I try to save the model.</p>
  
  <pre><code>import tensorflow as tf
  import h5py
  mnist = tf.keras.datasets.mnist
  
  (x_train, y_train),(x_test, y_test) = mnist.load_data()
  x_train, x_test = x_train / 255.0, x_test / 255.0
  
  model = tf.keras.models.Sequential([
    tf.keras.layers.Flatten(),
    tf.keras.layers.Dense(512, activation=tf.nn.relu),
    tf.keras.layers.Dropout(0.2),
    tf.keras.layers.Dense(10, activation=tf.nn.softmax)
  ])
  
  model.compile(optimizer='adam',
            loss='sparse_categorical_crossentropy',
            metrics=['accuracy'])
  
  model.fit(x_train, y_train, epochs=2)
  val_loss, val_acc = model.evaluate(x_test, y_test)
  print(val_loss, val_acc)
  
  model.save('model.h5')
  
  new_model = tf.keras.models.load_model('model.h5')
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "/home/zneic/PycharmProjects/test/venv/test.py", line 23, in &lt;module&gt;
  model.save('model.h5')
  File "/home/zneic/.local/lib/python3.6/site-packages/tensorflow/python/keras/engine/network.py", line 1359, in save
  'Currently `save` requires model to be a graph network. Consider '
  NotImplementedError: Currently `save` requires model to be a graph network. Consider using `save_weights`, in order to save the weights of the model.
  </code></pre>