title: Removing duplicate elements from a Python list containing unhashable elements while preserving order?
body: <p>I have a datastructure like this:</p>
  
  <pre><code>[
  [('A', '1'), ('B', '2')],
  [('A', '1'), ('B', '2')],
  [('A', '4'), ('C', '5')]
  ]
  </code></pre>
  
  <p>And I want to obtain this:</p>
  
  <pre><code>[
  [('A', '1'), ('B', '2')],
  [('A', '4'), ('C', '5')]
  ]
  </code></pre>
  
  <p>Is there a good way of doing this while preserving order as shown?</p>
  
  <p>Commands for copy-pasting:</p>
  
  <pre><code>sample = []
  sample.append([('A', '1'), ('B', '2')])
  sample.append([('A', '1'), ('B', '2')])
  sample.append([('A', '4'), ('C', '5')])
  </code></pre>