title: Cannot add layers to saved Keras Model. 'Model' object has no attribute 'add'
body: <p>I have a saved a model using <code>model.save()</code>. I'm trying to reload the model and add a few layers and tune some hyper-parameters, however, it throws the AttributeError.</p>
  
  <p>Model is loaded using <code>load_model()</code>.</p>
  
  <p>I guess I'm missing understanding how to add layers to saved layers. If someone can guide me here, it will be great. I'm a novice to deep learning and using keras, so probably my request would be silly.</p>
  
  <p>Snippet:</p>
  
  <pre><code>prev_model = load_model('final_model.h5') # loading the previously saved model.
  
  prev_model.add(Dense(256,activation='relu'))
  prev_model.add(Dropout(0.5))
  prev_model.add(Dense(1,activation='sigmoid'))
  
  model = Model(inputs=prev_model.input, outputs=prev_model(prev_model.output))
  </code></pre>
  
  <p>And the error it throws:</p>
  
  <pre><code>Traceback (most recent call last):
    File "image_classifier_3.py", line 39, in &lt;module&gt;
      prev_model.add(Dense(256,activation='relu'))
  AttributeError: 'Model' object has no attribute 'add'
  </code></pre>
  
  <p>I know adding layers works on new Sequential() model, but how do we add to existing saved models?</p>