title: what does numpy if the value in an array exceeds int8
body: <p>Consider the following piece of code:</p>
  <pre><code>test = np.ones((200,200))
  test = test*20000
  test_int8 = test.astype(np.int8)
  </code></pre>
  <p>When I implement this, I get that <code>test_int8</code> is filled with 32, why? and in general, if there's an array whose values exceed the maximum value that dtype I am converting into accepts, how does python handle that?</p>