title: Calling "fit" multiple times in Keras
body: <p>I've working on a CNN over several hundred GBs of images. I've created a training function that bites off 4Gb chunks of these images and calls <code>fit</code> over each of these pieces. I'm worried that I'm only training on the last piece on not the entire dataset.</p>
  
  <p>Effectively, my pseudo-code looks like this:</p>
  
  <pre><code>DS = lazy_load_400GB_Dataset()
  for section in DS:
      X_train = section.images
      Y_train = section.classes
  
      model.fit(X_train, Y_train, batch_size=16, nb_epoch=30)
  </code></pre>
  
  <p>I know that the API and the Keras forums say that this will train over the entire dataset, but I can't intuitively understand why the network wouldn't relearn over just the last training chunk.</p>
  
  <p>Some help understanding this would be much appreciated.</p>
  
  <p>Best,
  Joe</p>