title: Keras 2.0.0: how to access and modify the training data in the callback function "on_epoch_end()"?
body: <p>I am using Keras 2.0.0 with Theano. </p>
  
  <p>I would like to update the training data between each epoch. I can do it in a for loop using nb_epochs=1 but it would be much more elegant using the on_epoch_end callback. </p>
  
  <p>Here is my tentative code, based on a Keras 1 example(<a href="https://keunwoochoi.wordpress.com/2016/07/16/keras-callbacks/" rel="noreferrer">blog post</a>):</p>
  
  <pre><code>class callback_change_X_train(keras.callbacks.Callback):
  
  def on_epoch_end(self, epoch, logs={}):
      X_train = my_function_to_update_X_train(...)
      self.model.training_data[0] = X_train
  </code></pre>
  
  <p>Unfortunately, it seems that self.model.training_data does not exist anymore.</p>
  
  <p>Any help much appreciated!</p>