title: Python ctypes.Union
body: <p>What is wrong in this snippet of code?</p>
  
  <pre><code>&gt;&gt;&gt; import ctypes as ct
  &gt;&gt;&gt; class Uni(ct.Union):
  ...       __fields__ = [("sh",ct.c_short),("sh2",ct.c_short)]
  
  &gt;&gt;&gt; t = Uni()
  &gt;&gt;&gt; t.sh = 0x0102
  &gt;&gt;&gt; t.sh
  258
  &gt;&gt;&gt; t.sh2
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  AttributeError: 'Uni' object has no attribute 'sh2'
  </code></pre>