title: shuffle in the model.fit of keras
body: <p>In the <code>model.fit</code> of <code>keras</code>, there is a <code>shuffle</code> parameter,</p>
  
  <pre><code>shuffle: Boolean (whether to shuffle the training data before each epoch) or str (for 'batch'). 'batch' is a special option for dealing with the limitations of HDF5 data; it shuffles in batch-sized chunks. Has no effect when steps_per_epoch is not  None.
  </code></pre>
  
  <p>Assume the training set is a list with <code>50000</code> elements, so the whole list will be randomly permuted before each epoch? Of if the batch size is <code>250</code>, only the elements belonging to each batch get permuted? What should be the correct understanding?</p>