title: Python Pickling Slots Error
body: <p>I have a large instance that I've been pickling just fine, but recently I started getting this error when I tried to dump it:</p>
  
  <pre><code>  File "/usr/lib/python2.6/copy_reg.py", line 77, in _reduce_ex
      raise TypeError("a class that defines __slots__ without "
  TypeError: a class that defines __slots__ without defining __getstate__ cannot be pickled
  </code></pre>
  
  <p>I don't understand this error, since all my classes seem to define a <code>__getstate__</code> method, and none seem to define <code>__slots__</code>. I'm having trouble isolating the change I made the triggered this error.</p>
  
  <p>I can only assume there's some object nested deep within my instance that's causing this. Is there any way to get more info? How do I find the class of the exact object that's triggering this error?</p>