title: Why does a numpy array with dtype=object result in a much smaller file size than dtype=int?
body: <p>Here an example:</p>
  
  <pre><code>import numpy as np
  randoms = np.random.randint(0, 20, 10000000)
  
  a = randoms.astype(np.int)
  b = randoms.astype(np.object)
  
  np.save('d:/dtype=int.npy', a)     #39 mb
  np.save('d:/dtype=object.npy', b)  #19 mb! 
  </code></pre>
  
  <p>You can see that the file with dtype=object is about half the size. How come? I was under the impression that properly defined numpy dtypes are strictly better than object dtypes.</p>