title: Unique class instances in Python3
body: <p>suppose I have a class definition like this</p>
  
  <pre><code>class structure:
      def __init__(self, handle):
          self.handle = handle
  </code></pre>
  
  <p>How can I use <code>numpy.unique</code> or another tool of Python3 to find unique elements in a list of instances of this class? The comparison should be done with respect to the value of the <code>'handle'</code> field.</p>