title: (how) can you train a model twice (multiple times) in sklearn using fit.?
body: <p>Example : my data doesn't fit into memory can I do :</p>
  
  <pre><code>model=my_model
  for i in range(20)
         model.fit(X_i,Y_i)
  </code></pre>
  
  <p>This will delete the first 19 fit. and keep only the last one.
  How can I avoid this? Can I retrain a model saved and loaded?
  Thank you</p>